These are the settings I'm curious about:

by Tunable XML > Sims3.Gameplay.Objects.HobbiesSkills > NectarMaker
kgoodTNSThreshold = 1.1
kavgTNSThreshold = 0.9

In-game, they determine the result when a nectar making sim uses "predict combo effectiveness" after adding fruit to the nectar maker but before squishing it. I confirmed this by changing the first value a few times and getting different results for the same combo. I thought it might refer to the multiplier that determines the outcome (amazing, great, etc.) of the blend, so I raised the good value to 1.5 (the cutoff for amazing) and the avg value to 1.3 (the cutoff for great). The idea here was to actually predict the outcome.

The problem is, this value doesn't appear to completely correspond to the multiplier for the blend. The first two combos I tried at the new value that came back as "go well together" (the highest rating) ended up great, not amazing. Then I raised the value to 1.6, and one of the great blends, 6 avornalino plus 4 plums, still got "go well together." Meanwhile, 6 apple and 4 cherimola blan, an "amazing" blend when my sims make it, got the average response. The latter recipe does come out on the low side of amazing according to the value of the finished product, but it's still higher than anything rated as "great."

Anyway, if someone has an explanation for what these values are, I would love to hear it.

The notes in the tuning itself say: I don't actually know what TNS means in this context, though.

Buzzler at MTS seemed to have a good understanding of how the nectar process worked, as noted in Nectar Combinatorics. They don't seem to be active anymore, but you might find some valuable information in the description and by way of how the mod works.

Right, I guess the TNS here is just the in-game message. But what I don't understand is what value is being used: if a "great" combination gets "these go well together" at a goodTNSThreshold value where an "amazing" one does not, it's something other than the value of the blend, i.e. the multiplier that the hash algorithm spits out.

I do already know how the value of a bottle of nectar is calculated. My goal here is to find high-value combinations while playing with something a little more targeted than brute force. I'm not going to try every possible combination and was hoping to find a shortcut.

The problem with Buzzler's mod, and I do use it, is that it chooses the combination that will produce the most expensive bottle of nectar from among the combinations it simulates. It does NOT choose the one with the highest multiplier. So it only works well for finding new recipes when the fruits in question are similar in value, by which I mean not their cost but their weights assigned, from 3 for apple and regular grapes to 22 for life fruit.

I confirmed a while ago it's going with the highest-simoleon bottle by having some limited ingredients in inventory and watching the mod repeatedly choose a good (not even "great") combination that was worth more per bottle than an "amazing" recipe my sim had already made. I can probably find my notes from that time, but it would have been about 2.5 years ago, so I don't remember the exact combination I used.

In case you're wondering, I'd like "amazing" recipes because I want more of them and because they're the most efficient use of what my sim has already grown in his garden, mathematically speaking. I also don't want a garden full of life plants with a couple pomegranate trees and to spam the same recipe over and over; that's boring and if I just wanted the money, there are less-intensive ways to earn just as much.

Ahh I see, hopefully someone else may be familiar with the exact mathematics of it on the scripting side of things.

When I was looking for aesthetically pleasing recipes myself (using fruits thematically suited to the sims that were growing them, or just satisfying combinations of colours such as grapes of cold colours vs warm ones- so I relate to the desire for finding the recipes that make interesting combinations worth making) I relied a lot on a thread at Carl's Sims 3 forum where a lot of recipes were shared.

I could have sworn there was even a spreadsheet / Google Doc with a huge auto-calculated table of them that were sortable by quality, but I'm not sure if the link is in one of the replies there or if I saw it elsewhere. I'll keep rattling my memory around for where it might be.
While I was looking, I did find this comment there which, with the subsequent replies, covers a lot of it. Some of it was documented here but I think the full comments are a little more informative.

I've come across the thread at Carl's and have used the wiki as a reference for a while now, enough that I don't really have to anymore as I have everything memorized. If you do come across a Google Doc to that effect, I would absolutely love to see it.

All I can remember from my previous reading is someone posting the 20 highest multipliers (the outcome of the hash) and the 20 highest-value recipes when using perfect fruit. For the latter, some don't even come out "amazing," but "pretty good" plus eight life fruits is still going to produce an expensive bottle. It's not what I want though.

In case you're curious, what I want is "amazing" recipes that utliize a variety of fruits, because that feels more natural to me. I also mostly don't want recipes that use more than 4 types of fruit just because any more feels kind of messy, although I have a few with more that I can use for the moodlets. I don't really care to absolutely maximize the return on nectar making—like I said, I'd just have my sim grow life fruit and pomegranates and be done with it—but anything less than an "amazing" outcome feels like a waste. And because I'm kind of a completionist, I'm always looking for shortcuts to finding more good recipes.

Anyway, I do now have a substantial list of recipes, many of which I've read about elsewhere but quite a few I discovered on my own. Just testing gets really tedious though. Maybe if I go back to that, I'll tune the time required way down to make it easier, but I'd honestly rather have a guide of sorts to tell me what to try, then go from there. And by "guide," I was hoping that changing the TNSThresholds would be my magic shortcut.

If anyone does want to see some recipes, just ask.