My local GP recommended massaging the scar tissue for about 5 minutes twice a day - very gently, very briefly, and at a different time from dilation. He said that would help it heal without constricting (and it's his suggestion to anyone with major scarring, not specific to GRS issues). It really worked surprisingly well; I went from significant pain at entry to essentially zero, although it took a month or two of the massage before it stopped hurting entirely. My guess, and it's ONLY a guess, is that since you didn't have trouble for the first month, that "first inch" problem is probably scar tissue tightening up and not the pelvic bone - since the bone and the pelvic muscle have been there since the beginning. 🙂 Apparently, depending on how quick someone heals, the scar tissue goes from healing-and-flexible to starting to contract around the 2-4 month mark.
I also use an applicator (like they sell for yeast infection creams) to get lube deep inside before I put the dilator in, because a lot of lube was getting scraped off at the entrance, and that helps with the last inch or two.