Have you ever looked into the Hell's Gate series by David Weber+Linda Evans? Its setting conceit is a multiverse linked by planar rifts/gates between parallel worlds, and what happens when the inhabitants of two different universes - one with steam-age tech and psi talents, the other with medieval tech and magic - encounter each other and end up going to war. One thing they quickly learn is that the more 'verses they move from their home universe, the weaker their respective powers get, and vice versa.