Small Grid Conveyor Junction + Frame Changes
Drop small conveyor ports, replace them by medium.
Make fully airtight.
Add small conveyor ports to the sides.
Similar to this mod: https://steamcommunity.com/sharedfiles/filedetails/?id=341588634
Just both 3x3 sides would have medium conveyor port.
Or add new blocks with these properties.
Changes to these two blocks would increase build flexibility.