Flashing in a tiny gap – GreenBuildingAdvisor

I’m a first time poster so I hope this is an appropriate question for your board. I’d really appreciate any help you can offer.

I’m hoping to get advice on how to add flashing to a small gap. I’m remodeling an attached greenhouse in Maryland. The “roof” of the greenhouse will sit just below the soffit of the main house. It will have a 3/4″ gap that is set back about 12″ from the top and 21″ from the bottom (please see attached drawing). I am leaving this air gap to deter humidity from the greenhouse from entering the attic. I do not want this gap to be any bigger to maintain growing space in the greenhouse and simply because it looks much nicer without a large gap. I’m planning to have the roof of the greenhouse be cement fiber panels (As I will probably have a lot of extra material) . The roof will have a slight pitch to shed water away from the main house.

Options I’m considering are:

A sealant that can be pumped or sprayed in with an extension hose (Maybe something like “Great Stuff”?). Then take a tiny corner squeegee on a stick to seal it against the seam.

Or, attaching peel and stick flashing to the back side of the greenhouse roof material and overhanging it by an inch.

Then angling the panel as it is positioned to lay the overhanging flashing against the back / vertical wall of the main house.

Then using a 3/4 “ square pole to reach in and press the flashing firmly against the house?

Thank you for any advice!