Dihedral's a funny thing...just the right amount can stabilize a plane in the roll axis, while going above or below that amount can have "other" effects. I'd be, however, a bit leery of the idea that the lesser dihedral OF THE TWO SUGGESTED BY THE KIT would produce a MORE stable airplane. This isn't to say it WON'T, just that it's a bit counter-intuitive.

My immediate question, however, would be "How did you determine the cause of the crash was a faulty control horn?" The crash you describe sounds very much like an airplane that simply didn't have the airspeed it needed, and stalled. Now, please understand, I'm NOT saying "that's what happened", just that the description WOULD fit that scenario...so, essentially, i'm asking "how can we be certain?".