Rounding of an edge with a hanging strop is a myth, there are countless treads on this. There is or maybe some convexing of the bevel with any strop and possibly more so with a hanging strop. Convexing of a bevel is a good thing, strengthening the edge, not a defect.

The amount of convexing of the bevel is so minimal, flex in most strops even those glued to a hard surface will give enough to reach and polish the edge. If in doubt paint the edge with a sharpie and strop. If the ink is removed you are reaching the edge. It really is just a matter of preference.