I was thinking about your case specifically earlier. I think there may be a few things at work but who knows, all that matters is that it works for you.
My guesses in no particular order:
1) didn't need really high doses to get to where you got (Luki said as you mentioned)
2) ED dosing of even longer esters seems to work better holding mg constant (shouldn't but does for many and backed by bloods)
3) You've held a lot of that muscle for a long time (not calling you old!!). I think the body creates a set point that's hard to breach over time especially if food and lifting are still in place. (just my Bro Science but matches what we've all seen I think - caveat is no one's set point is 270lbs @ 6%)
4) Genetics, maybe in muscle, holding muscle, and/or response to lower doses.
Could be all, some, one, none but it works so ultimately doesn't matter.