increasing .renderScale causes framerate drop (Gear VR)

Hi
I have a GearVR (Galaxy S6) for my project. When I increase the render scale to 1.5 the image looks much better, but when I get close to objects, the framerate stutters. Even in a low poly test scene with no textures.
When camera is at a medium / far distance everything framerate is perfect.

In my profiling - the v sync seems to take a big hit.

Any advice?
Thanks,
Glenn.

 

solved it - I was (stupidly maybe) using standard shaders, rather than mobile shaders for my material.. everything runs perfecty now at higher render scale.