That's one way,another is to use two pieces of the mould to make one.By that I mean rip the first piece to an inside 22.5* with the long point of the mitre touching the wall(if it's 2.5" from the reveal you want at the window to the wall angle then cut it that wide overall)then rip the second from new stock making up the total width of the moulding(if the moulding is 4" wide then the second piece would be cut 1.5")by cutting it on the same inside 22.5* and putting the mould back together.You must cut the 45* angle(that picture frame the window) on the pieces as well before you rip them to size.Basically what it does is just turn the corner following the wall.The header and bottom mould must be cut on the same angles also starting with two pieces.
Man that's confusing:blink: I wish I could show you but it looks good