Isolation 3-bet range?

[VBCurtis]

1/2 6m, seat on my right is a 98/48/1.0 after 50 hands, with an 18% win at showdown. Rest of table is decent-TAG, with preflop stats averaging 25/10. My image is similar at the table.

Suppose you are the cutoff, and the fish has open-raised. BB is a 20/18, no postflop read yet. What is your 3-betting range?

Am I right to think that since he raises 50% of hands, 3-betting our top 25% means we're ahead of his range? It seems we're +EV to play anything ahead of the midpoint of his range. Is that too tight, since we're better postflop also and have position?

-Curtis