When you have a max weight including the fuel, the guy whose plane is on the heavy side will be forced to fly with a small amount of fuel, possibly causing a flame-out. So in that way it is easier for the weight rule to specify empty tanks.

When I last flew with a glo motor I used the OS140. It could do a pattern on only 10 ounces of fuel. This is 300ml, and weighs about 260grams. Does a YS170 use much more than that? So 5500g total allows glo planes to increase their weight by maybe 200g, and electric planes by 500g. I think this would be a big relief to everyone. There would be less need for using tiny receiver batteries, or ultra light carbon props, etc

Neil