I can offer a suggestion if your willing...

if you want uniformity of a shape around an object, then use the initial object, make a selection from it, grow the selection to teh inside edge that you want and then you can edit the selection (alt/ctrl to remove/add to a selection). That's how I do it. Just remember to smooth once you have expanded, not sure how best to use the smooth option but normaly at the size you expanded by seems to work best