it seems that every 15 ranks you stop getting a tier (within a well)
so at rank 15 you stop getting t1, at rank30 you stop getting t2, and I assume at 45 you stop getting t3, but no one is there yet to confirm it
for whistling lower level monsters: it appears that ~10 levels difference is the range that you can still get drops at, but past that it's horrible to nonexistent
This post was edited by Dante on Dec 13 2016 06:05am