Thanks for your advice! We have tried to make it clear which part of shadow players can stand on, but we can't think of a nice solution, and the only thing we could do is to make platforms that might confuse players to not casting any shadow.
For the second piece of advice, well, since many levels already have multiple light sources, I guess you're hoping to see multiple movable light sources —— this is possible, but we failed to design levels that are interesting and contain multiple light sources. Perhaps we'll figure out how to do that in the future.