Repurposing FX busses as mix busses on a MR18


I have been using two SoF busses for a vocal buss and then an instrument buss with its compression side chained to the vocal buss to make room for the vocals when the vocals present themsleves in a busy mix. I also need 6 auxes as monitor mixes. It occurred to me today that I could repourpose two FX busses serve as the other two monitor mixes. I set it up in the GUI but haven't had time to test it out yet. I'm wondering of it would be better to use the FX busses as the vocal/inst busses and keep the native busses on monitor duty. Any suggestions?