it's actually more on the how big the penises player perceive/fantasize them to be than how big the penis are in the portrait (unless you put the characters side-to side naked in the CGs and portraits). Putting dick size means putting a clear standard to compare the size of all characters.
I just thought it's quite weird for multiple characters to have the same penis size (8 inch). Lex in particular has the biggest physique, so some people like me imagine he'd have bigger if not the biggest size instead of the same as Ragnar's. Maybe like 10 inches or so ;)