The recommended psi differential between regulators is 200psi if you want good consistent air flow. Most of the volume of any air flow is directed towards shooting the ball, and LPR air flow is not quite so critical because not much air is used. Therefore, I wouldn't worry about the input pressure to the LPR as long as the input pressure to the LPR is a bit higher than the LPR output pressure. So, if your Angel required 150psi chamber air to shoot a ball, then it would require 350spi at the input to its HPR which is 350psi output from the tank regulator. Anything more than that will give you even more air flow.
The only real problem with the HPR on Angels is that they don't have much range. If you are putting a high pressure tank regulator into it, you probably won't be able to adjust the velocity into a usable range. I changed the HPR on my 04 Angel speed to a Bob Long Torpedo. It had better adjustment range and allowed me to use all of my HP mag tanks on my Angel. Any good inline regulator will allow you the same full adjustment and may be an easier option than keeping another tank around just for your Angel. The same is probably true for the Tribal.
Except for the Automag in front, its usually the man behind the equipment that counts.