With time to have thought about this i realused there is another component to stack and string angle. I havent seen it mentioned but perhaps its already understood. Either way, i just recently realized it.
String angle is not what matters with stack. It is tip leverage and that alone. String angle is a bi product of leverage, not the cause of it. For example, the longer the bow the more leverage the limbs provide, as a result string angle is low at the tips.
Lets take this further. A short bow with standard recurves. Whats standard, I dont know dont be so difficult, just humor me. Now the recurves provide more leverage at the tips and as a result, the strung angle is low.
But lets complicate things. Why? Because I like to be difficult, and you arw still reading this so it must be ok with you too. Lets say for illustrative purposes only we have a short straight limb bow with no recurves. We know what to expect with string angle at its tips and stacking already regardless of how long the short bow is you just imagined. Now lets tie on a recurve the diameter of a basketball, and make it so the tip ends 90 degrees. When strung, the stack reduces as well as string angle. Lets now untie the basketball sized recurves and tie on soup can ones, same 90 degrees. All else being equal, the stack will increase compared to the basketball, even though string angle is identical. Now lets tie on a recurve the size of a golf ball. Once again all else equal, the stack will increase compared to the soupcan, but string angle is the same.
The take away here is, with tips, its a leverage function. With recurves, the leverage increases with radius. The string angle is just along for the ride.
Now the next stwp is to realose, there is an optimum radius and angle for any bow. Find that and you have a winning combination. Im certain there is a ratio or formula to be made to calculate the perfect tips for any bow.