I'm wondering if there are any good guidelines for how much pressure there should be in the filter for pool circulation.

I have just replaced the motor on our pool circulation pump (bearings finally got too noisy) and the replacement went faily well and I have the new motor working. I noticed, however, that the filter pressure reading was different than I expected with the new motor. It is rated to be a 1:1 match for HP and RPM (3/4 and 3450 respectively). I have previously replaced the seal only a while back and had a change in the pressure reading as well. At that time, I could not seem to adjust the impeller clearance to increase the pressure which I thought I had to do even though the flow was good so I left it alone. This time, I changed the impeller clearance to drop the psi to about 15 psi since that seemed like less strain on the equipment and the pool return flow seems strong. It got me wondering though about what the pressure should be for a balance of good flow and safe operation. I have some leyway with the impeller to make it higher or lower if there is an advantage.

Any tips?

Thanks.

Background:
When we took over the pool: 17 psi baseline
When I changed just the seal: 14 psi baseline
When I changed motor and seal: 20 psi baseline

Pool: 20,000 gal. inground, indoor
Pump: 3/4HP Pentair HydroPump
Filter: Sand - Tagelus TA 60D (does that indicate the size?)

There have been no other changes to the pool piping or equipment.