Selector Valve Position?

My inground ANTHONY (SYLVAN) pool has a vertically mounted brass selector valve. Normal operation has this brass valve all the way down. When I backflush I would turn valve 90' and pull selector valve halfway up...that is what a pool guy told me to do. It always did backflush the filter OK. Now I read that the valve should be pulled ALL the way to the top most position.
What is driving this post really is what position should this valve be in (halfway up or full top) to help lower the water level about 3 '.
Thanks much, Tony

colby - I don't think it really matters. I got rid of my push-pull a few years ago, but seem to recall that as long as it is NOT LOCKED DOWN the water takes the correct path. If that makes any sense.