The height of the collection cup doesn't seem to make much of a difference. I currntly have it not quite all the way down.

I'm not sure if I understand the mod. The pvc tubing is glued to the lid so that it also fits over the riser? I guess this makes the bubbles slide down the pvc, between the pvc and the riser? Right now, the bubbles just spread out and stick to the lid. I guess I can try your mod.