Tivase,
I do generally focus on a single angle at a time. Whether one “should” or not is really an open issue. With all the attention IPR training protocols are getting, I wouldn’t be surprised if the optimal strategy is to mix up different angles. You could, say, do BTC on Mondays, Wednesdays, and Fridays, and SO Tuesdays and Thursdays. We really don’t have enough data to say what works best, so feel free to improvise!
Regarding your question about ligs versus tunica work, one should first recognize that all hanging angles hit the tunica. The question is whether the stress you’re applying is intercepted by the ligs or extends all the way back to the pelvis. Hanging at low angles will interpose the ligs. Hanging at high angles will generally keep the ligs out of the way.
I think you want to do some of each. Whether you want to mix them on different hours, days, or weeks is up to you, but I think the best results come from a varied approach.