Return below or above the surface.

[SilverSwede]

I have seen two designs on the return line from the column(s) (whisky column, vodka column or gin basket or quite commonly these drain into a common line) back to the pot. In one of the designs the return enters the pot above the liquid line in the vapor zone. I have heard by the people that promoted this design that it has to be that way or the still becomes vapor locked and floods if the return is under the liquid line and to never fill the still above the return line entrance point. 

On the other end I have heard that if the return line is above the liquid line vapor will enter the return line and "fight" the returning liquid.

Interested in  operating and engineering opinions, pros and cons with both designs.