CFL Foiler said..
.... I highly suspect the Flow is stable because the canopy is always under tension no matter the bar trim, which means it has less depower range than the BRM. .....
I think you've got all that back to front.
The reflex profile on the D-Wing means the rear lines can be completely unloaded and the wing can come as far forward as it needs to. The reflex automatically counters any tendency to collapse.
A classic profile the opposite happens. The wing comes forward, the A-lines carry less load and the wing collapses. Tensioning the rear lines can make it worse.
The downside of the reflex profile is the wing is a bit less efficient. The D-Wing makes up for that with slightly more size and a more substantial leading edge.