Actually you are exactly right on the SD percentage. Wallace is more dwarf than Caesar. Wallace is only 20% mainland. His dwarf percentage is 43.75.
Another thing I have been thinking is my small rats may be the size of your mediums. The place I get my rats from tends to have larger sizes compared to other places. The larges I get are really big, and the XLs are enormous. I actually use rabbits for my boa and skip the XL rats.
10 feet is not big if he stays lean. My carpet is 7ish feet and I can easily one hand handle her.
I'll bet our retics are close in size to be honest. I just can't measure Wallace because he's a freak.