I think for a bottom, the PSA wouldn't be affected if you don't have a prostate anymore. Plus, if you have had lots of post-op monitoring PSA tests without knowing this and wouldn't be able to say for sure that you have never received anal within a week of the test, it is better to carry on as you are.
There is lots of anxiety about things like orgasm, cycling, anal stimulation affecting PSA but most of the data is about the possible impact of prostate stimulation - if there is no prostate, what is there to stimulate? It seems to me that the most important thing is to try to be consistent before tests - behave the way you normally would. Perhaps the day before a PSA test is not the best time to buy a bike and go out on a 30km bike ride, have anal sex for the first time ever, etc.