The bloodwork displays testosterone in a ratio of testosterone to blood volume (nanograms per deciliter.)The same amount of testosterone will show up as a lower reading in a larger man because he has a greater volume of blood. A 6'2" 275lb man will have roughly 55% more blood than 5'4" 165lb man, and his bloodwork is going to show proportionately less testosterone.
Before judging how good of a responder someone is, or how accurately dosed your gear is, you need to have an idea of how large the user is.
I put it like this. The top guys at the Olympia are going to have to use more than 500mg of test to maintain or grow in their prep.