You know, I was just dealing with this today. Every time the F trip comes on I let it go 10 or 20 miles and fill up, but I usually only get 3.5 to 3.75 gallons in there and it holds 4.5. So today I let it go to 175 miles total, (33 F trip) before I put any gas in. When I stopped I could still here some gas splashing around in the tank. When I filled it to the bottom of the filler hole I put in a total of 4.0 gallons. But then I slowly added a few squirts at a time to the top, and then it settled back down to the bottom of the fill tube. I did that several times until I had put in about 4.25 gallons. I was able to squeeze in that .25 gallon and didn't get any spills or overflow on the bike when riding it. That's the most I've ever gotten into the tank.
In my opinion, you should easily be able to do 30 miles of F trip. Maybe a little bit more, but you'd be pretty safe with 30. Next, I'm going to carry a pop bottle filled with gas, just to see how far I go before I'm out.