I did my first install on mulions a couple months ago.
New artist designed graphics for our building... It was 12 windows tall. Our unique logo was placed smack dab in the center of 4 WIndows... So it had to go over mulions or itd look dumb.
The windows were about 10ft high where the logo was... I placed it,did all the windows... Came down and from floor level it looked so un-aligned. I thought I messed up... Reprinted / cut the mulion... Took me 5 tries to make the angle look right when you stand right in front of our building. It looks off if you're standing anywhere else... Including driving on the road.
Everyday I want to rip the whole thing off and redesign it.
Doesn't help you, but I'm just throwing another hat into the don't do it ring.
But if you just have to do it...Best way up do it? Print/cut the mulion section by itself with a few inches extra in each side. Apply the windows like normal cutting away where the bars are.... Then once your done go back and use your extra pieces to align it at whichever angle you get the most foot traffic.
Then after spending an hour getting all the mulions done... Show the persistent owner how bad it looks unless your looking at it straight on, and charge $100 to remove all the mulion vinyl