If you have a set of comply T-500s, use it BUT cut off the extra bits of foam that protrude past the rubber core. I get the best seal using that system, as there's no air pressure/vacuum seal involved. I find it actually brings out the treble more for me with unvented iems like this.
I appreciate the suggestion and I'll give it a shot in the future when I'm back in North America.
Having tried all the various tips included with the N4 I've settled on the smallest of the blue. The red and bi flange work though comfort is poor. I question if anyone will get a good fit with the included foam.