All pics again from the awesome Trek Caps -
https://pic.star-trek.info/index.php
A couple of observations about La Sirena interior size and layout.
It does extend beyond the main cargo hold.
When Picard is first brought on board,the EMH emerges from an open section "stage left" (first pic)
Further this section extends even further back behind the wall that contains the circle of light emitters.
(second and third pic) over the EMH shoulder there is a cut out on the panel, which is not mirrored on Picard's side.
This also reveals that corridor extends well behind the wall with the lights.
If that is the warp core housing, that is likely where any "engineering" room is and any drama might play out with another EH reveal - an Emergency
Engineering Holo..
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From E.4
A similar (storage?) room opens up on the other side..
As well as an open panel for tools, weapons?
And looks like another ladder down to the second level.
Also on both sides left and right seem to be what could be hatchways, that likely open to the exterior, maybe corresponding to the rectangles on the side of the ship, between the cockpit and the wings.