There are many different ways that a bolt can "misfire". So long as the center of the string travels in a way that will keep it pressed against the center of the end of the bolt, it does not much matter what the brace height is.
The danger which Todd mentioned is that a low brace height can sometimes cause the string loops to get over the upper shoulders of the nocks. This will cause the string to leave the bow, and the prod limbs to continue traveling forward unchecked. The resulting stress reversal is decidedly prejudicial to the life of the prod. Indeed, an organic prod might fail right then and there. Therefore, this particular mode of "misfire" should be guarded against.
In general, I think you will find that if you lower the brace height a bit, the increase in friction of the string on the top of the tiller is more than compensated for by the longer stroke. That is, so long as the string still has tension in its resting position.