there is also an assumption made that when ejecting (with a clear hex behind the mech), the mech must've been standing close enough to the edge of that hex to get the pilot clear of whatever else in is in the hex (such as a building).
That's a really good point I think. However, TW p.167 states that units spend mp to explicitly enter a building. "Note that the rules in this section cover entering building hexes below the level of the roof; i.e. movement actually inside the building in a hex." (The rules on the attendent piloting skill rolls are more ambiguous though and state the roll is made when entering a building
hex.) It's also impossible to physical attack into or out of a building hex. TW pp. 171 "Physical attacks cannot be made against targets in a building hex by units outside the hex, unless the attacker is located in the same multi-hex building and is adjacent to the target, on the same level of the building hex." I think it's reasonable to state that a 'mech in a building hex is
in the building. As such:
Star League Building Code: 341.2: Structures must contain one or more skylights per 900 square meters of ground floor.