Walls and Ceilings - Molding Problem

I have a Cape Cod home with window dormers in the front bedrooms. I am putting up a molding just down 8 inches from the ceiling so that the room will look larger as this makes it look like a larger ceiling. However when I come to the front dormer the wall from the ceiling there is slanted 45 degress and this makes the molding surface area larger than on the flat wall. the molding on the wall is 2 1/2 inches width but on the 45 degree angle it becomes 3 1/8 so of course the molding doesn't match up. I cannot find a similar pattern that size. does anyone have a solution or suggestions. Thanks.

There might be a geometor who can tell you what to do.

This is custom work and you need to contact someone who does custom wood moldings. Problem is how to match up at corners.

Welcome to the forums! With any turn of molding, whether it be 22.5 degrees or 45 degrees, the angle causes the wood surface area to increase. But if you cut both pieces at complimentary angles, they will match, regardless of their new width. You may want to follow the wall to within 8 or 10 inches of the dormer, then 45 down, 45 back across at a lower level, then continue the molding through the dormer, and do the double 45 where it exits the dormer on the other side.
Not sure if this helped any, but posting a picture of your project on a site such as photobucket.com may help us to see what you are up against, and then we can give better advice.