I'm told that putting the return in close proximity to the pick-up, (such as is found with an add-on sump or is common with fuel cells that provide two fittings side-by-side,) offers a high possibility of creating a swirl in the fuel---such as is found in a toilet bowl. THIS IS NOT DESIRABLE.
With a pressurized return, such is found with EFI, the 'head' is not as critical as it is with carburation. In a carbureted lay-out, the head will cause fluctuations in fuel pressure and is considered a 'no-no'. The Holley guys suggested an 'above the fuel' position for the return line. Holley EFI has the pressure regulator built into the throttle body and set at the factory. Although it is field-adjustable, a 'head' will, to some degree, interfere with the factory setting.
My methanol fuel cell has one of the side-by-side fittings capped. The return goes into the top of the cell where the return fuel goes directly into the foam and velocity and potential aeration are thereby dissipated.
KS