Thanks for the info!
I was just thinking about that - you need to try every soluiton, there is no other way.
Aaand, that's how you end up like me with hundreds of keyboards and thousands of switches. It is true that in order to fully evaluate you would need to try all of the options.
Top mount, sandwich mount, tray mount, leaf spring, gasket mount, 0-ring mount, metal case, plastic case, wooden case, ceramic case, silicone case, PE foam, plate foam, case foam, tape mode, force break mod, stabilizer type and mods, lubed switches (oil vs thin grease vs thick grease vs a combination), lubed springs, filmed switches (poron vs PC), tactile switches, linear switches, clicky switches, every combination of every type of switch bottom and top housing material, all switch stem materials and pole length, every length of spring in every weight, keycap profile (MT3, DSA, SA, GMK, MTNU, DCS, DSS, etc..), keycap material (PC, ABS, PBT, POM, etc..)
And there are a lot of things I'm probably overlooking. Imagine the sheer number of permutations there are and almost every single one results in a different sound.
Sometimes, you have to tell yourself it's okay to be content with what you have. Know there may be a better solution, but there are also many worse.
However, for generalizations, a "thock" sound is often true each of the following:
Softer switch bottom housing material (like POM), lubrication with grease, light to moderate spring weight, long-stem pole, using 1.5mm or thicker keycaps, cases that keep the bottom of the keycap slightly recessed below the bezel, a non-metallic case that has some resonance in the bottom (not too stuffed), a stiffer yet non-metallic plate (something like FR4)
I found when looking for a good deep thock sound that some of these above listed options actually took the sound too far into a muddy, dampened sound. For instance, grease is great for toning down clacky switches, but if you accidentally get too much on the stem pole, it might result in an uneven and muted thock. And POM is a great housing material, but again, it can actually sound limp and muted without the proper stem, spring, and lube setup.