Normally maximum bed thickness
Is determined by the adhesive manufacture .
Question is this a bad job or are you researching for future work .
Maximum weights for background also come into play , more adhesive more weight.
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Yeah it's more to do with the shrinkage and weight than the bed depth. So different adhesives (manufacturer and classifications) will have different bed depths. I don't think there's an actual minimum or maximum thickness. The tile just needs to be either fully covered (100% for floors and wet areas) or mostly covered (60-80ish % for kitchen walls I think it is).
I think it has more to do with size of tile and using the correct trowel. Like 1' X 2' LFT should use trowel with 1/2" NOTCH and you should back butter tile @ least 90% for walls
This is what is going to determine your thinset thickness. The size of the tile determines the notch size of trowel.