Their lights are blocked by the earth's surface because the flat earth is traveling >> Downwards Universal Deceleration AKA DUD (the better version of Universal Acceleration).
Try to draw a diagram. If you do, you will see that bends light in the wrong direction.
If the light initially heads out "horizontally" relative to us, the acceleration (which you call downwards deceleration) would results in the light bending down relative to us.
This would make celestial objects appear higher, not lower.