I was advised to rivet in my windows
in a cross pattern, such as one might use for tightening the lug nuts on a wheel. One center left, then one center right, top right corner, followed by lower left corner etc. all the way around.
I also only pulled the rivets snug to allow the butyl tape to squeeze down, then later went around and put another single pull on the rivets. Let it settle some more during the heat of the day, then came back and pulled another single pull. Eventually the rivets started to "pop" and I went around doing them all.
The frames may be a less than perfect match for the wall curve, doing the rivets a little at a time allowed me to tighten more where it seemed to need it, and allowed the butyl tape time to get squeezed out so the window frame would fit tighter against the wall.
YMMV but that seems to have worked for me.