A larger bore tip (larger hole) will create more air and treble, it can also effect the soundstage. I wouldn't recommend going for a smaller bore than the supplied Hybrid, Usually by using a smaller bore you can funnel the sound and drop highs a small amount and bring bass up. but you're at the limits I would drop in bore diameter. What you want to find is something with the similar size bore as your Hyrbid but a touch longer in length. That will allow you to tame the highs a little further. You could also try Comply which will cushion the high end a touch. Possibly a triple flange will help you out here. Or a triple flange with the longest section cut off.
have a look at some options.
Edited by H20Fidelity - 11/7/12 at 10:43pm