I would answer that there is probably a greater chance of fire disaster, but with any tank we live with that chance all the time- still a smaller tank could minimize trouble. When I thought about going longer distances- finding some distant used car for instance and going to pick it up, cause I almost never go farther than a 6 mile round trip in my area-
I considered taking some extra fuel along in a plastic bottle, I could dump into the tank when needed and then dispose of- simple!
there are 2.5 liter and gallon tanks (4 liters I guess) but that's going to add weight and then more likely get in the way of your legs if you pedal.
A 1.5 tank was standard with kits before I started back in 09, and then the larger 2.5 was more common for a time but now they've gone largely back to the 1.5. I like a smaller tank myself, and with baskets front and back and a trunk bag otherwise- and I usually wear a cycling jersey with the three back pockets, carrying another liter or so in an empty soda plastic. At 61 my MB mileage is dwindling considerably .
The other option then is a rear rack mounted tank and I think they hold more than the smaller front tanks. I'm still waiting for a small plastic tank that would fit a cruiser frame in the usual old tank way, but the oil controlled forces are not letting that happen. Industrious shop boys haven't graduated to "Plastic" I guess or just want more power and more fuel.