I have one pipe coming from the suck side of the pump (between the pump and the boiler), leading along then up to the expansion tank. It goes straight into the bottom of the tank, and there's a T just at the tank with the over the top one you describe.
I fail to see why that pipe is less resistance. Water pressure is measured by the height of water above you, which is identical inside the tank and in the loopy over the top pipe.