It could be placed higher if you wish but since it is a Primary secondary loop the primary loop is always flowing and under pressure it will carry any air to the Spiro vent where ever it is placed, more important is it's spacing from anything that creates turbulance, circs, 90's and the like, the goal is to get the air to settle to the top of the piping and slow down going into the air seperator so it can be vented, the golden rule I use is no turbulance within 18 inches of the vent, this is not as needed with a Spirovent type air seperator like you have Larry.