Perhaps you could add an Earth / Walls reading to the Scan window when examining / targeting? That wouldn't quite solve the problem but I think it would help more than having to open the description window to check every tile.
Main problem with that is that it would be
constantly updating the scan window when you're moving the cursor/examine indicator around, which is annoying.
It
would, however, solve the other annoyance of having to always check terrain armor explicitly, since that is basically the main number you'd want to know if you're trying to get through a given terrain but aren't sure whether you have enough firepower...
Maybe terrain could be different and that one would only update on a delay? For example only after you stop moving the cursor for 100ms. I like this idea...