Mines has been very adaptable, and it's helped. I don't really mind it, though I understand your worry. I worry about that with any type of friend in my life, I'm worried that I'm manipulating someone to be how I want them to be. Or that they'll do something for me even if it's not something they'd want to do on their own. Had a very aggressive/dominant first gf. But she also changed herself to anything I commented on but wasn't necessarally a complaint. It made me feel controlling.
But back to my T, the first T was kinda triggering and when I brought up things that bothered me she only explained it was her methods but didn't seem apologetic or like she'd be willing to change. So my knowing the T I see now adapts to be who I need her to be, is very important.
The only other thing is, sometimes I can feel her hesitation or something that she's holding back. Like maybe she's dials herself back during our session. This is where it gets a little difficult because my mind sees it as being her not being genuine and reverts to doubting her.