You should shift into the large-large combination and confirm that the rear derailleur can accommodate this. If the chain's too short, it will bind and stop the pedals. If the rider does this while riding, they may tear the derailleur and/or hanger off! (As me how I know! OK, I'll tell you. I set up my mountain bike with a short cage derailleur way back when to "be cool." I knew not to shift into large-large. Just a quirk of my bike. But when I let my uncle ride my bike, I didn't remember to tell him this and he had no idea about avoiding large-large, so he did it. And I had a two-piece derailleur thereafter!)