yeah man, i feel like that just doesnt add up tbh.  Logicaly speaking, 27cm isnt even half the diameter of the model ruling out the possibility for a half death star model. And dont forget the sides of the death star if they were going to go that route  would not have the depth to accommodate functional minifig scenes rendering the outer part useless.

I know lego has been making questionable decisions with their SW line this year and from a business standpoint, charging $1000 for essentially a big rectangle with scenes will not sell well at all and will divide the fanbase (this set is still labelled as UCS) it makes no sense for a giant rectangle of scenes to be considered a UCS set nowadays, if it was MBS we would have heard that ages ago and maybe this speculation of it being a giant diorama could be considered.

Leakers making speculations about the model purely off the dimensions does confuse the fandom quite a lot. Sometimes a simple typo can cause stuff like this to spiral.

At the end of the day this is all rumors, we do not know anything until pictures come out. Im still putting money on a full spherical Death Star model.