Make the spell of reflection a directional beam rather than always being directed at the caster. You can still hit yourself with it, but you also have the option of giving a monster temporary reflection. The beam stops at the first monster it hits so it can’t multiply the effects.

If you cast the spell of reflection while already having reflection from the spell but after you’ve gotten a message indicating it’s running out, you get the full duration of the spell rather than the reduced one.