Yes, you describe the sound well. Most speak of the bass but it's actually Z1R treble that makes it the best all rounder I've heard, in my opinion. Both fits are 'correct', I can use Sony S tips for a deep fit, or M tips for a shallower seal. I get a good seal on both (easy to test seal, use a track with bass drums like Hotel California and check that they hit like they should).
As long as you're only inserting the nozzle up to the teardrop ridge on the shell, you're doing it right. Try shove it any further, like some people oddly try to do, and you'll have all sorts of fit issues. Look at the shape of the shell - the teardrop bulge just below the nozzle corresponds with the same cavity shape in our ears. It's literally designed to 'slot in', but you can also push it slightly further out with a larger tip if you don't mind the earpieces balancing on the tip itself.
As above, yes you can get a good seal.with both, one deeper, one shallower. Most say treble is less splashy with a deeper fit. I wear it that way because it's more comfortable and the nozzle is thin enough to do so. With IEMs with thicker nozzles I only have a shallow fit as an option.
