I guess Sea&Sea japanese engineers do not follow this Forum... unfortunately!
Maybe because the battery compartment stays underneath it, just like the tripod socket used to attach the tray...
Having used Sea&Sea for 10y now, one of the things I like most in their housings in the way they design the tray adapter, it is very sturdy and firm with even the heaviest lenses like the 14-24mm!!!
I never used the new plastic housings, but the answer you seek might be in this area.
Trays should not only prevent the camera from pointing downwards with the lens weight, but also sideways as you use the controls.
I don't think I ever saw a DSLR housing with the ability to change batteries while the adapter is on, unless the battery compartment opens to the side.
And in your case I recommend you don't leave it on the camera. The locking mechanism is different from the MDX housings, and the "lock lever" sits with no support when the camera is out of the housing. IMHO it's prone to brake.
Good Luck!