Don't use the ball option myself, preferring instead to leave a good sized foam tag off the front end thus:
They absolutely slaughter trout on my local stock ponds. My theory is that the profile of the white foam is to some degree lost against the lightness of the sky when viewed from below. certainly when I tried some tied with black foam, they weren't nearly as effective.
That said, there's really no point in going for more foam than is necessary to hold the emerger in balance in the surface film. Over buoyancy will cause the trout to 'miss' when taking as the very buoyant fly is more likely to pop out the side of its mouth on the stream of water pushed to one side as the fish head and tails over the fly. I've seen this happen when I've tied the tag in slightly too long. Trimming it back a mil or two usually rectifies the situation.
Hope this helps,
Matt