Only the pump outlet will be facing down if i use any of these configs
that is not good... as u can get a bubble stuck at the top of the impeller chamber and have a moment where the pump can run dry.
the outlet must be facing up with inlet sideways so bubble can escape top.
or sideways with inlet up... so bubble can escape out back though inlet from the top.
Visualize a bubble...they always want to go up, but can be stuck in a chamber or cavity...
can it escape in the config if it was stuck inside the chamber?
Will your pump run dry?
if u can say yes to any of those questions... then the pump is located in the wrong position.
EDIT... the only time u can sort of ignore this is if u have a redundant pump system and your first pump is in a location where it will never run dry.
Then you bleed with the first pump... and then activate the second pump some time after.
You probably dont want to bleed with both pumps on anyhow... as too much flow will just chop up your bubbles and make bleeding longer.