The SM's have a map of the area why and how?
Immediately, because the Imperial Navymen, unlike the invading SMs, can simply call up any section and say "Hey, we have enemy invaders in Sector 7G, we can't repel them. Jettison the block."
Right, you mean you'd have to have the psyker read the mind of a crew member to find out who his boss is... and then read his boss' mind to find out who is his boss, and so on and so forth.
BTW you still haven't presented evidence that this is a standard battle tactic or examples of their scans working through jamming fields or being so accurate.
BTW how far out can the Terminator squads teleport? Because the Death Star, during the Battle of Despayre fired on the Fortessa from a distance of 2,209 km.
Until the area is jettisoned into space.
Without specifics I have no way of knowing if this was smilar or not. Oh wait, I just read about it. The World Engine was already known by the IoM, they had enough info to deduce that a regular attack would not work, and sacrificed a Battle Barge to destroy land the Space Marines, and then used the Imperial Navy to actually finish the job.
They don't need a map of the area. All they need to do is get a general idea of where the populated areas are and smash through with boarding torpedoes.
With hundreds being deployed all at once, ejecting every section they land in would be difficult. The storm troopers would not slow the SMs down in the slightest. The transmission would go like this: "We have invaders in section 7G. Jettison the bl-What?? they moved to sector-hold on they split up....." and so on and so forth. The doctrine of the SMs is lighting warfare, moving faster then the enemy can react. At what depth can they jettison sections anyways?
With 20-30 psykers working at once it would be fairly quickly. all you need to do is to find someone who knows how, or knows someone who can, switch off the shields, or the super laser. Once again the DS's critical systems are the ones giving off the most energy and would be fairly easy to locate. If it wasn't standard battle tactic, they wouldn't do so well in space battles now would they? Any ship generally need an idea of what they need to shoot, otherwise they go down easily.
The terminators can teleport from high orbit, which is in the neighbourhood of 5753.9 miles or so, which should be sufficient.
Once again, how many levels down are the DS able to jettison and how long would it take? There's really nothing on board the DS that would pose much more then a negligible distraction to the terminator.
And I actually just remembered one other little trick librarians have up their sleeves. Machine Curse. Working together they could shut down nearly any mechanical device they wanted to. I doubt this would extend to massive structures such as the power core or the super laser, They could just as easily shut down anything onboard that the SMs could specify, such as the mechanisms that jettison sections, blast doors, life support systems and so on and so forth.
Also remember how they destroyed the World Engine in the first place. Should all else fail, they can always smash the ship into the DS and deploy every soldier on the ship. The ship itself would be damaged beyond all repair, but in the end the DS would be annihilated from the inside out by a legion of invincible super soldier.