Mount it in the cockpit on the foot well bulkhead, just aft of where you normally sit, so you can reach it from your steering position, but not so far forward that it would interfere with jib sheets. The top of the throttle just below the seat. I mounted mine a little too high, the top of the handle a little above the seat, and it would sometimes snag my short pants legs.
Beside being able to reach it from your normal sitting helm position, it should be accessible if you are standing and steering with your knees. Don't mount it on the coaming.... that's inconvenient if you're steering from the opposite side.... plus it looks ridiculous.