I am going to hazard a guess by saying what you're doing is similar to cap averaging except your going frame by frame and using opposite techniques to find a middle ground?
The combined shot of Han above looks nice but it also loses the detail from the second shot while retaining the dark of the first shot.
Maybe with some tweaking and playing you'll come up with something that can retain the best qualities of both and not be blown out.
Cheers for your effort.