Been there, done that. You are lucky to have an ortho who is not frightened of arthrofibrosis (internal scar tissue formation) and is not hesitating to perform the best possible technique for dealing with it. It was so validating later to have described to me scar tissue obliterating all areas of the knee; it had migrated into the femoral notch of my TKR, up into the quad, and there was a 1/4" band of tissue tethering my quad to bone. When I had the procedure done, my ROM was steadily going backward!
Just a warning: I came out of it with an ROM of 10/85 degrees; he said he got only 0/95 degrees "on the table" which means under anesthesia and completely relaxed, so that number represents the max. For a few weeks after there was almost no improvement, and I sought a second opinion, and that doctor offered no hope. But I tell you, my self-designed PT program worked. For a month, I did only stretches, and kept them gentle (they could be uncomfortable but not painful, so less than 4 on the 1-10 pain scale). I would sit on an exercise ball and slowly roll forward, thus bending my leg, and held that stretch 30-60 seconds. I would do 10 of these 2-3 times a day. That's all. It took a month before I got beyond 90, and when that happened it was like I passed an important marker and became encouraged and more patient and kept gaining. You have to be careful not to push a knee prone to arthrofibrosis because many believe (as I do) that PT can actually make it worse. Anything that hurts the knee stimulates more scar formation. And keep up on your pain meds and icing. I had to do extension efforts too. They hurt more and took longer to get there, but I would have my husband gently push down on my knee with a pillow behind my knee to cushion the effort as it didn't take much to make it hurt like crazy.
Again, you are in good hands, and know that this is the right path and it may take more time than you might expect.