Ok....sorry to muck up your question with all those unwarranted examples.
To recesses the Screen housing to where it's Flush, you need to both allow for the room to mount it, as well as factor in the amount of "Drop" the screen has available, as it will relate directly to the positioning / height of the Projector's Lens.
Your getting a w1070, so at least you'll have some vertical Lens Shift capability, but you only want to use what you absolutely need to. Also, the w1070 has NO
Horizontal Lens Shift, so the Lens will have to be virtually perfectly aligned "side -to- side with the Screen center and edges.
Here is a Flush mounted, recessed screen assembly. While it may be in a build-down enclosure, and not in an actual ceiling, it's still the same principle.FrontSide
Up inside the Custom made Slotted InclosueDown through the Slot.
In your situation, unless you have attic access above the Screen assembly, you would have to construct a removable "slotted" panel that is held in place using "Bullet Snaps", and make the enclosure at least 2' wider*
than what is needed to accommodate the width of the Screen's casing...which is always at least a solid 12" wider overall that is the actual Screen material that retracts up into it.*
to allow for at least a modest upgrade in screen size and / or type.