Another downside to bottom placement is whatever barrel length extends out beyond the light is casting a shadow upward in the worst possible location. Starting with lights on ARs long ago when there were fewer mounting options and bulkier lights to get any kind of lumens, I developed the habit from experimentation of running lights on the right side which also kept it from banging into me (right-handed so on sling AR left side hangs against from of body), and got used to functioning around that barrel shadow being cast off to the left.