I would suggest DeoVR, you desperately need a horizontal stereo offset setting for JAV VR because most videos are off. Usually you need to increase the offset. I find it easy to focus on the background objects and adjust the offset until my eyes can focus on them without problems. This will help fix scale problems.
In most cases you also need to change the zoom, usually zoom backwards a bit.
Is there a DeoVR for Samsung GearVR? I can only find versions for cardboard and daydream, but this app seems to have some very useful options.