I do actually struggle to range people when they flat the SB it's a bit of a strange position that I should really look into. What range do you put him on when he flats pre? Do you think he's donking any of that range? Villain has plenty of 5x and Jx, maybe discount AJ and KJ a little I assume, probably not all that often does he have JJ+, things like 66-TT maybe slightly discounting some of the stronger hands there. Bar that his betting range as played on the turn is mostly FDs I'd assume which can make up a large part of his range.

That's all guessing though.