Why not use the 900 preflop to raise to 1200? If he shoves you fold and your in same position. I suspect your 900 bet after the flop was very transparent with that flop? He knows if your betting the 6 he will push you off and if you had 10 you would most certainly check to the raiser. He had position so call preflop and fold post or put your 900 in early.