Partially blaming catheter was because when they've pulled it out for the first time I was able to go a tad deeper. And yes, I know it shouldn't be it, but maybe it's pushing on something else. Pelvic bone was a really good guess, I thought it might be it as well at first, but it doesn't feel like a bone at all. Just a tough/swollen tissue.
My dilatator is 1.4inches thick and metallic, so it's not flexible. Maybe I should start thinking about something smaller, but that one was recommended to me by my surgeon who's name is Jarolim BTW, but I doubt you would know him, because he's from Czech Republic (here we have SRS fully covered by insurance, but only if it's performed by a local surgeon).
I'm getting the dilatator in just like you are describing :-). I thought it might be issue as well (at first I've kept my legs spread), but it only helped a little bit - I've felt few muscles to loosen up a bit, but it was inconsequential in the end.