i found that some tips effect sound as in if they allow the iem to move or wiggle you can lose the bass and mid range. I find if i push the tip deeper into the ear i get more bass so i ended up going for the double flange initially to get a deeper insertion. However the double flange felt like i had a football wedged in my ear after a while so settled for the single flange.
Also if you care to look back through a couple of pages i mentioned similar findings to what you described though not in your detail and I was advised to give it burn in time but me being me I bought the galaxy silver cable and it took away all the trebly/sibilance that was annoying me.
BTW what are you using as a source and are you playing flacs - all those observations could just as easily be a source issue - try another player if you havent already
EDIT: just been reading about the effect on sound that different tips make over here
http://www.innerfidelity.com./content/comply-foam-tips-and-effects-tip-selection
well worth a read