Holleys aren't as bad at this, but Mallory pumps cannot pull uphill at all. The grabbing the fuel from the pump inlet side is an electric pumps hardest thing it has to do, anything you can improve here will help the pump. You have the trade off of low enough so the fuel isn't being sucked uphill at 1/8 tank, but high enough so it isn't sitting underwater when you have a bit of water in the boat. You want the shortest fuel line you can get, optimally 2 pumps, 1 at each tank. Failing that, one pump on the transom will split the difference between the tanks and will be the best compromise (and will still work)..
Mechanicals have the opposite problem- they can suck the tank from a long way away but have issues pushing that fuel out.