I check mine in the same spot (inside the shop floor) and I know one is requiring more oil than the other.
Hummm... ... ..... I always use the same filter too. That couldn't be it.
I just changed the oil in the 90 a few weeks ago and am now getting around to checking the level inside the shop. This one always shows the same thing right after an oil change... ... ... ... ..... One quart low.