Would the string angle be the red one or the blue one?
DC, it is the blue one. That is the only one that makes sense for comparison, as it fit's with experience. We know the recurve makes a difference, that string angle makes a difference.
1. You will only find ONE angle to measure similarly on a straight limbed bow, the two angles are one in the same on a straight limbed bow.
2. The red angle is effectively the same as if the recurve was not there, so similar angle would not explain the difference in how it feels when pulling (the difference in stack).
So there it is, the blue (ie: as close to the point of contact as you can measure, almost infinitely so).
This is for common statics, i suspect you'd have to treat working recurves and very drastic recurves a little differently, but similar principles apply.
Now, if we'd like to get into a discussion of the physics of why there is a difference, I'd be glad to put my physics teacher hat back on and present that in another thread. Some have skirted it here, but not nailed it down.