Don't want to get into a family dispute here . . . but if you control water depth, temperature, and exposure to wind (via a low bucket top, relative to the pool) . . . the bucket test is reliable.

Period.

I have close association with some pool techs, and they are ALWAYS in too much of a hurry to do finicky little tasks correctly. Route-based pool service profitability lives or dies by pool call brevity. So, at least for the pool techs I know, it is probably true that "bucket test is only reliable if you are seeing large differences of at least 3/4" or more". But that limitation is not intrinsic to the test itself.