The actual percentage of filler blend varies across rg's.
You'd think it'd be dictated by trying to keep the same %age of each tobacco, but it's not. The amount is determined by the size of the leaves the roller is working with.
The filler is dictated by the least amount of wastage.
That's why a certain cigar will come in certain sizes and not others.
If a cigar becomes popular enough (sells well enough with a high enough mark-up) to introduce a size that requires a lot of wastage, then they'll go ahead and add it to the line and see how it sells.
What Tyler said about the corona, I've heard the same.
Some cigars can end up with the same percentage of fillers, like maybe a corona and robusto have the same percentage of blended filler, but the size throws the wrapper ratio off.
If I find a cigar I like, I try to smoke as many sizes as I can until I find the one I like best. A lot of times the best cigar is the corona, but I like a larger rg and settle at a beli or toro or some larger ring, even though it may not be as good.
It's fun to try as many sizes as I can get my hands on, and usually I'm not disappointed with any of them, but one size sometimes is remarkably better (to me) than others.