Strategies for closing FBM “promise gaps”

Long time seller here.

About 70% of my sales are FBM.

I watch my seller and fulfillment metrics like a hawk.

I ship 100% Standard shipping for free. I have zero day handling. My regional shipping templates are all set to the minimum delivery estimate allowed for each region.

Currently my “promised delivery time” is 7 days.

My “actual delivery time” is 4.8 days.

This gives me 2.2 day “promise gap”

Amazon tells us that decreasing this gap may lead to additional sales, and encourages us to do so in the strongest terms possible.

I feel like between 0 day handling, free standard shipping, etc that my “promise delivery time” should be much less, or at least closer to my actual time.

I do not have SSA enabled. I did a quick test with it last month and it created absurdly long shipping estimates. But maybe it needs more time/data to become accurate?

Does anyone have any experience with successfully (or unsuccessfully) closing the promise delivery gap?