I usually put in somewhere between 3 and 3.5 gallons, but I do feel it's a lot easier than a sportbike to fill since I sit a lot lower and have my feet flat. And really, I don't suppose that I feel it needs to be straight up, I just like doing it that way and am a nerd like that I guess.
I've only owned a few motorbikes in my 25 years of riding. I'm super impressed that you've had 30! Definitely a little bit jealous of that :)