As we discussed earlier, it is dangerous for a Defender to make a decision - to abandon one Objective to save the other. This is the decision that the Invader wants to force the Defender into making when there is no time to think through the consequences. But how can the Defender know what decision is best?
The Defender, in order to make a wise decision, must have total situational awareness. This can only occur if his team is constantly communicating with each other, telling each other what they see happening in their part of the map. The Middle Team Defenders especially must be fully aware of what the Bravo and Alpha Team Defenders see, so that they will know where the major push is taking place and where they are needed most.
The map you forge must provide this environment for the Invader to exploit. This in turn will force the Defenders to cooperate and communicate to achieve total situational awareness if they wish to overcome the Invaders. This is the essence of Dual Territories in Invasion and you really should have this in your map to be successful.
A very clear example is Boneyard Tier 1. Notice how the Bravo Defenders can wind up in the Bow to hold off the Bravo Invaders before the Invaders have a chance to enter the Lobby or advance upon the Bravo Objective. Both the Middle Team and Alpha Team will not have any eyes on what is happening in the Bow. Creating chambers, rooms, or pockets of areas where the Defenders cannot see each other or the firefights that they are all engaged in will force such communications if they wish to achieve the total situational awareness that they should need to win.
Gentle ramps, partial elevations, other general level design concepts can help in creating a lack of LOS between Fire Teams, forcing them to communicate to maintain total situational awareness. These forged features also lend to good level design in general, increasing the fun factor for the vast majority of players.
Summary
Territory Tiers have exceptional play when the Defenders cannot see each other, and must rely on communications to maintain total situational awareness of what each Team is experiencing.
Creating chambers, rooms, and other forms of LOS obstructions forces the Defenders to communicate if they wish to overcome the Invaders.
When done correctly, these pockets of isolated areas can be joined together to form a very fun play ground.