The placement of vertical stabilizers are nothing to do with RCS. They must be angled for low visibility, not 90 degree like we see on f15 or MIGs. I think the placements are more related with flight performance
AFAIK When designing stealth platforms one must avoid 90 degree angles in the geometry whenever possible, wherever it can. And those stabilizers do look like they mounted with an angle of 90 degrees on top of those engine humps.As far as I'm aware, there's no reason the location of those stabilisers should adversely affect RCS. Their location has little to do with the engines or RCS, they are placed where they are due to aerodynamic factors like vortex flow from the nose-inlet junctions. Because Kaan's engines are further apart than the F-22's to make space for the rear facing radar/electronics complex, the stabilisers end up being on top of them.
Ill wait for the 2nd prototype to appear, and comment accordingly