There is already a system in Place that calculates how many tiles there are between a pawn and its target. This could be used to create a hit percentage based on range. One solution for partial cover could be to have certain obstacles that block a custom trace channel, so if the regular visibility trace is not blocked but the other trace is you could reduce the hit chance.
Yes, it clips through stairs with steps shorter than the tile width at the moment. There are several possible solutions to this problem, and I’m currently trying to find out which one would be the cleanest and most efficient.