Higher string tension at brace height is my understanding.
The string is accelerating the arrow more strongly as the string nears brace height than a bow with deflex. I've heard this tends to exagerate errors in form.
Seems like it would work the same as a bow with lower brace height vs. higher brace height. The lower the brace height the less forgiving.
Honestly though, I don't find a whole lot of difference except maybe between the most extreme cases, i.e. a hill bow with string follow and a reasonably brace height vs. a short static recurve with the tips 4" in fron of the back of the bow and a 5" brace height.
You're thinking yourself into a state of paralysis. Don't worry about it so much. If you're going to try making a highly reflexed bow, lack of forgiveness in shooting will be nothing compared to the lack of forgiveness in tillering.