Well now, with 4 3/4" I'm not exactly very deep but I guess passable - yet I know about rectal pressure also.
Going straight in with the dilator did in fact compact my bowl contents, believe it or not.
I'm now pushing more upwards after I reached initial depth and it seems to help.
Healing will add some too, I guess, as I'm now in my 4th month post-op and seem to be able to push more upwards - it was too sore in the beginning (at the vaginal entrance stretching toward the anus), I might have lost some depth due to that.
It was a feeling, when dilating, as if shoving the dilator more up my colon, hitting that 3rd sphincter and it left me always with a feel of not having evacuated my bowls properly - yet nothing would come out (bowl contents).
So, I'd say, dilate more upwards once at initial depth, and healing should help also with the discomfort.
Take care,
Axélle