stacked units

Hi everyone, It's my first post here, so I apologies if something like this was suggested before. Background & Rationale Now, I've been playing this game since CIV II, and unlike some, I think CIV VI has brought some amazing depth to the game, especially with the 1UPT rule. It makes combat...

The civ I'm playing is Arabia. During a war with rome I send over all my Mamluks since they are great. I have one corps and one unit (both Mamluk). The corps is right under a Roman encampment and the lone unit is standing to the left of the corps (See image). I selected the lone Mamluk to attack...