Some time ago I heard that trimming the leading edge of the Mylars would help bending it at the leading edge of the wing. There are some ways of doing it and I've seen some pictures of tools put together for this purpose.
The one I used does work but the trimming has to be done in one single pass. If it gets stuck in one specific Mylar part it will melt the Mylar and create a nice hole.
I used this
carbide cutter from Dremel.