I prefer mine on the side of the fore-end above a vertical grip but everyone's different. Get something non-permanent like cable ties and try it in a number of places and see where you like it best
When I used one I preferred the switch on a vertical grip, though that’s only because I put the switch for my PEQ on the 11 o clock position on the rail. If you’re not using a laser then that’s where I would go, sits perfectly for your thumb