what exactly do you mean by "a rock" = his post-flop play is exclusively fit-or-fold?

ok, pros and cons of flatting pre-flop.

con 1 - there are no short stacks behind
con 2 - chances are good that you're going to see a flop multiway and without position
con 3 - you abandon a bunch of dead money
con 4 - you're playing against ranges you are unsure of


pro 1 - disguises your hand
pro 2 - keeps fish in the pot, but a 3-bet likely will as well.

after flop actions,
utg range is something like JJ/AQ+/KK/KhQh
MP 1 range is any ace, any flush draw, any pair, any set.

Raise flop, don't be folding. Why? you're betting for value against both players, and to protect your hand. How much? $20 is a nice number