If the commode is setting level (as it should be), the water level at which no more water will remain in the bowl is the top of the internal trap.
No more water will stay in the bowl because the water is overflowing the trap, that’s the water line in the bowl. Either it is designed that way or it is defective.
I have seen some commodes designed so not much water is in the bowl. That’s one way they meet the 1.6 gallon per flush and have enough water to wash the sides of the bowl.
Measure from the bottom of the visible trap to the water line, then measure from the top of the bowl to the water line. Eljer should be able to tell you how close this is to their design water line height with one of those two measurements.
[Edited by Jerry Peck on 13 October 2000]