Should there be any standing water left in the sump?

This is a basic GE dishwasher approx 10 years old (GSD3320C06BB). I was having standing water visible in the tub after finishing (about an inch). I used suggestions offered here in other posts and now it is draining much better. However there is still some water remaining in the sump (I have the sump covers/protectors off). You would not see this water if the covers were in place. Is this normal? I've read elsewhere that some water is supposed to remain so that pump seals don't dry out. Or perhaps I have a check valve in the drain system that isn't functioning correctly. Parts diagrams do not show any check valve so perhaps it would be embedded in the hose or pump itself? Observing the drain cycle, it appears that most of the water is pumped out of the sump as it runs but as soon as the cycle ends, and the pump shuts off, some water flows back into the sump, stopping just before reaching the tub itself. Otherwise the drain flow into the disposal seems to be very strong now. Thanks.