Ichon

If temp is the main concern then by all means as you are correct heat rises. I haven't had an issue with heat even fairly aggressive OC but I do live in an area where I rarely have to use AC even in the height of the summer so that makes it a bit easier. I was more concerned with dust and noise than heat but go ahead and try that vortex idea out. I think there should probably be a bit more of an angle on that forward top fan to encourage spin as it kinda slams into any mounted drives but I don't really see a big issue with heat if you do have the upper grille open or if there is you probably shouldn't be air cooling anyway.

I have that case and it is pretty quiet but a bit crowded so will require good cable management to really maximize airflow but I would start with intakes where there are filters on the front and use gravity to help on the outflow at the bottom. Air should move in one direction from the front to the rear with perhaps a fan at the bottom to push out that you clean more regularly than anything other than the filters. My R5 is going on 2+ years now and barely any dust build up with the upper grille closed. Those are some huge holes with not much of a filter on the top so unless you are doing something not described in the OP it doesn't make sense especially with the R5 where the main logic would be having a quiet setup I'd think? Having the grille open at the top sorta defeats that idea.