That's the difference between an airbox (no lid, just the box and a proper high flow filter lock wired on) and open carbs. The loss of power between 10 and 11 probably more than canceling out the gain further up.

To be honest I though that it felt best with the lid (with and a couple of holes in) on, a thought confirmed when I rode my '28 racebike back in that format before I sold it the other day.
In fact it was that good I'm going to put a wanted for an '18 airbox in the classifieds in a min.

On the other hand, the fact the box isn't there (and in the way) might encourage you to jet the bike correctly, thus getting the power back where it should be
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