I don't consider myself to have very large ear canals, although fine outer ears that fit buds fine. I recently got the Triple.Fi and am finding tip choice to be very important. So far, the stock tips suck for the most part. The foam is pretty crappy, and the only other tip useful is the small one. The double flange and medium and large single flange tips are worthless to me. The foam is junk and not taperred (which is very nice to have) I ordered Shure Olives and some Comply T-500s to try out. I've used the Olives in the past, so I'm familiar with them and do like them a lot. They are a significant step up from the stock foam that came with Triple.Fi.
As for structural fit, I think it takes a little getting used to. Part is the tip you use, and part of it is the orientation you place them in your ear. I tried both over the ear and not, and both work fine. Comfort is more dependent on orientation though, so if you've got them in at the wrong angle, it may end up resting against your ear somewhere. I ended up back over the ear again, but I'm planning to grab some Phonak Audio silicon molds that come with the PFE. It wraps around the wire and makes it more comfortable over the ear. It took a little tweaking of the memory wire to get a decent fit over the ear in the first place, and a silicon covering will simply improve upon it. I think the experience will improve considerably once a good tip is used.