Actually the prefered location is on the side. That's why they are called sidelights. On smaller vessels they may be combined into a single light on the centerline.HI ben. While I'm familiar with the set up you're going for, I'm not sure it's actually legal. I know several rather prominent manufacturers mount them this way, but I'm not sure it's correct. As I understand the regs, both the red/green nav lights are to be mounted on/near the bow with a visible range of 112.5 degrees each for a total of 225 degrees. You'll also need an all-white stern light visible in 360 degrees. By placing the nav lights on the helm not only can they become more easily obscured, but they may not have the proper range of visibility either. I would triple check the regs to be sure.
(b) "Sidelights" means a green light on the starboard side and a red light on the port side each showing an unbroken light over an arc of the horizon of 112.5 degrees and so fixed as to show the light from right ahead to 22.5 degrees abaft the beam on its respective side. In a vessel of less than 20 meters in length the sidelights may be combined in one lantern carried on the fore and aft centerline of the vessel, except that on a vessel of less than 12 meters in length the sidelights when combined in one lantern shall be placed as nearly as practicable to the fore and aft centerline of the vessel.