Just letting one Arbites die is better than losing three Space Marine units and relinquishing the forbidden fortress anyway.

The units taking the fortress may now be in a good position, but remember there can only be three units in there, setting up a massive counter attack from both adjoining outer palace sections. Dorn will still get his bonus and Sanguinius' ability will counteract the fortification bonus. If both Traitor heroes moved into the fortress then the counter attack should at least kill the odd chaos space marine unit to break Mortarion's and Magnus' ability combo.

Not too mention that if that was the traitor's first move then Lion's Gate spaceport will be left relatively undefended too. You could deploy one army or tank unit in each of the adjacent areas to give you a good chance of at least one not corrupting to allow Khan to counter attack the spaceport. Leaving area between the spaceport and the fortress south of it (where Khan would be) so he cant be blocked off.

Divide and conquer.

Of course, he may just wipe out the Arbites and not move in. Or just with the warband to destroy a laser battery if there.

Or you could deploy enough pressure around the other spaceport that he has to act with them first. Or just risk the combo and have backup. Or fill the fortress with Custodes instead. Etc. Etc.

Three Headed Monkey said:

This most likely wouldn't work. In Scenarios 2-6, with the Titans generally tucked away inside the Factories, there aren't any must-bombard areas like in scenario 1 (the area with 2 Titans + 2 Tanks). With Space Marines hiding in fortified areas as well, that just leaves the Spaceports and any other areas to the pre-game barrages. Corruption + Bombarment I feel would clear the areas. Not to mention that Primach + 2 Chaos Space Marines would most likely be enough to hold on to the Spaceport (playing defensively), then just Port Landing for 12 combat ranks of reinforcements, with Khan now sitting out in the open or Drop Pods to Khan's area.

Dam said:

I suppose you would have to be lucky, but I dont think its outside the realms of possibility. You have four places to put units around the spaceport (leaving one empty so the khan cant be blocked by a corruption). You might as well take the opportunity and force the Traitor to use his bombardments on single unit areas.

How would you place the Imperial Army and Tank units in scenario 2? Massed and defending the plateau?

Besides, you dont have to attack the spaceport. Even if he is defensive, his forces will be split. Cue mass assaulty, including Khan, on the forbidden fortress. Or you could just hold out. Forcing him to put more effort into setting up a massive force for assault due to the stacking limits in fortified areas.
 

Actually, after the two Spaceports, assuming they both didn't turn fully over to the Traitors, bombardments (usually 1-3 left out of 4, one of the Spaceports generally gets targetted) are against single unit regions, because A) the Imperials don't mass their troops and B) all the juicy targets like I said are in hiding. Scenario 3 is even more likely to see bombardments against single unit regions, with 6 of them to allot. Of course, Traitors like to snip Imperial Fists Monastery and/or Forbidden Fortress as impassable in Scen 3 if possible, limiting the Imperial Palace to just 5 areas, forcing the Imperials to mass in a smaller area, meaty targets in all.