Target Champions only Plus Ground Attack Move Click

I bought Kalista a couple days ago after having played her in ARAM a few times when she was free and doing really well with her.

So now I've been testing her out against the AI just to get some mechanics down, and I've noticed I can't use target champions only with my ground attack move click at the same time.

In ARAMs I never used Target Champions only as the minions were gone so fast it was never an issue. Against bots though, I'll be trying to target the champion and my allies will get them low and I'll press rend and it will do nothing because I've only hit minions EVEN THOUGH I've been holding the target champions only key down the whole time.

I've tried rebinding the key to \ (my keyboard has this slash in two places, the one beside ; as normal and one beside left shift) and changed it to A as well when it didn't work thinking it may be because I had two of them. Neither time was I able to target champions. Hell, I made a custom game and would be behind enemy Lucien's minion wave using target champions only clicking past him while I was closer to him than the minions and Kalista would run and go attack a minion!

Does anyone have any idea what's going wrong here? Does Ground Attack move prioritize minions even if I'm holding Target Champions Only? I'm just really confused on how to make this work as nothing I'm trying is working and obviously I need to be able to attack champions before I start playing her against players...