The problem I see is, that he thinks he already has gained her affection by the time of William's promotion. I don't think at this point he thinks he needs to attack her indifference. He didn't know she was indifferent at the proposal.

I previously called him Collins-ish and stupid for ignoring her NO to his proposal and only seeing modesty. You previously said "She practically ran away screaming." I agree, he should have understood!

But he didn't. ch.33 post proposal interview
Fanny knew her own meaning, but was no judge of her own manner. Her manner was incurably gentle; and she was not aware how much it concealed the sternness of her purpose. Her diffidence, gratitude, and softness made every expression of indifference seem almost an effort of self–denial; seem, at least, to be giving nearly as much pain to herself as to him.
...
that to a temper of vanity and hope like Crawford’s, the truth, or at least the strength of her indifference, might well be questionable; and he was not so irrational as Fanny considered him.

In my previous post I quoted showing that he thought he had her affection already. I still can't help thinking he was stupid and irrational even though the narrator has said he wasn't "so irrational". I think the swelling in his head may have blocked the sound of NO from reaching his eardrums.