I have a fork crown mount for my headlight... (+ trekking bars) cape over hands but not over light.
[wired led]
another bike has straight bars ,battery light on front rack - its the snow bike so parka is fine,
the water is a solid then ..
I have seen cycle rain capes made with a clear plastic window for the users of handlebar lights to shine thru..
a window like that can be sewn into yours perhaps?
since then I have changed to an LED headlight .. (hoop shadow, insignificant)