The tunica and especially the septum limit the bananas girth and length. It's a connective tissue (collagen) a type of protein. Collagen is still a stetchy material but also the most robust inside the penile tissue. In theory, pumping the corpus carvernosum and corpus spongiosum will not yield any gains except better bloodflow/cell regeneration if unable to weaken/stretch/denature collagen and create more space for growth. Erectile tissue that fills with blood pushes against the tunica and therefore is limited in expansion by how far the tunica allows to stretch.

Collagen starts to denature at around 37 °C. This could explain why I was successfully gaining with Bathmate. I measured the temperature of the water inside my Bathmate at around 40°C. My skin was able to tolerate a temperature of up to 43°C when 45 °C became painful. (Also, the higher the water temperature the higher the chances of blisters/edema/burns.)
For my new routine I'll focus more on heating up and not pumping with Bathmate to maximum. Probably going to pump 2 x 10 mins sessions with refilling the tube with hot water after the first 10 mins to maximize heat. Going to try to avoid edema as much as possible to not damage my frenulum.
The ultrasound device (US Pro 2000 2nd Edition) heats up to aprox. 35 °C which is great for comfort and helps counter ambient temps. I don't like hanging or using a pully system because of privacy and ambient temperature cooling of the banana. Using extenders while wearing pants helps for warmth. (thinking about heatpads) Ultrasound will heat up collagen and allow a much longer and more relaxed stretch.
Going to use a vacuum cap and stretch around my quads to work the banana with ultrasound. I'm also going use ultrasound while strapped into my extenders. (Leluv Slider/X4 labs) The extender rods will only allow ultrasound application to work top and bottom. I'll have to experiment and see which approach is the best for me. The first 20-30 mins of extending will be enough to warmup and get into the zone. Then adding in ultrasound should have a great effect.
Using ultrasound can also help to enhance the pelvic floor while shockwave therapy probably has an even higher chance at doing this.
Aiming for high quality 3-4 hours of extending per day/5 times per week and Bathmate + ultrasound with 2 days off in different intervals. Cialis 2-3x per week (max 10mg) has proven to be very effective for regeneration, flaccid/erect bloodflow and much stronger/more frequent morning wood.
There's also a chance that ultrasound may help against plaque tissue causing peyronie's disease. Maybe it will help me straighten my left curve.