My bet is that difference between gravitational waves and gamma rays due to the effect known as "surfing". A gravitational wave pushes light back from peak, whe

My bet is that difference between gravitational waves and gamma rays due to the effect known as "surfing". A gravitational wave pushes light back from peak, where light is slower, to bottom, where the speed of light is normal again. The difference between gravitational wave and gamma rays is more dependent on initial magnitude of gravitational wave, than on distance traveled.