Mine fills about half way on a multi-hundred mile day but not full.
I have @ 4-5% fuel in oil after 800 miles so I've been changing my oil at very short intervals as it loses viscosity very quickly.
If you haven't I'd get a oil sample checked as you may have a bike that has a high fuel/oil percentage. If you leave it in for 2500 mile intervals those last 1500 or so may have some really degraded oil. If you notice any gas smell when you change it I'd get it checked. Regular oil like the 15-40 that Spud uses or Rotella T6 that I use isn't expensive to change on a short interval. I don't change the filter until 2500 miles.
A quick drain valve is in the future for mine. 1350ml fills it without a oil filter replacement. It's a quick thing to drain and refill without a filter change. I use laboratory 1000ml griffin beakers to measure all kinds of stuff for bikes, way easier to measure and pour than the plastic bottles! They cost about 10 bucks.
