I tried these out looking for a new IEM. I found that the Monster MD Trumpet tips work perfectly, giving a much wider option in terms of comfort. The original tips really hurt my ears, I was thinking I would have to send them back. Great sound, too much pain though. Just felt nasty (all three sizes). Pulled out the Trumpet box and tried a smallish pair of tapered single flange silicone gray tips, immediate relief, sound still fantastic. All there. The Trumpet are large microdrivers, so they have a very large sound tube, and it is large enough to cover the massive KEF tube but not enough to slip off and remain in your ear. Excellent phones, though.
As for isolation, with the Monster tips they isolate as well as any other in-ears I have owned, which is limited. But no noise issues and with these tips they feel like a deep insertion headphone. Not so with the OEM tips.
Happy to see that you passed like me with success the possible fit issue!