So I've been looking for clarification on how you actually "assault" a Skyshield if there is no room for you to get your model up there. It looks to me (and I hope I'm missing something) like there is no way to assault it per the RAW unless you have room to physically place your model up there if assaulting from the ground.
The only rules I have found about this deal with Ruins and the Skyshield is most definitely NOT ruins. It isn't a building. It isn't battlements. It is "unique" with the top being treated as open terrain and attempts to move onto it (or assault one presumes) rough terrain. In the case of Ruins if there isn't space you get to assume you are in base to base contact, running up stairs (what have you). No such rule or Faq/Errata seems to exist for the Skyshield.
What this would seem to mean per the RAW is that a line of enemy units blocking your forward motion (you dont' get to move through them) will prevent you from assaulting them period. Obviously Jump Troops and the like can get up there if there is room, moving over opposing units to open space during movement to then assault, but short of that I think you are stuck out in the cold. Is there a rule, faq, or errata I'm missing somewhere?