Bro Spawning is a fundamental Game Element in Invasion, so naturally an Invasion map needs to make effective use of this feature. An Invasion map should promote Bro Spawning with significant value to most any offensive strategy. An Invasion map should reward Invader Teams that regularly use Bro Spawning, and reward Defender Teams that regularly prevent and interefer with Invader Teams trying to utilize Bro Spawning in the Forward Position.
Bro Spawning in a Forward Position allows an Invasion Team to asssert their presence closer to the Objective. Without the time to recover from an offensive push, the Defenders are kept off balance and less prepared to thwart an Invading Team. Controlling a Forward Position, therefore, becomes valuable to both Invader and Defender alike.
Forward Positions are areas of safety that the Invader Team can fall back to when their push against an Objective is unsuccessful. We say that they fall back into the Forward Position, because typically the Invader passes through effective Forward Positions on their way to the Objectives. This design allows the Invaders to case areas as they move toward their Objective, identifying areas they think would make good fall back locations if they get into trouble. It is unreasonable, for example, for a forger to expect an Invader to plan to use an area on the other side of the Objective, an area they do not know about when they first play the map. This is also true of Forward Positions along other routes to the same Objective.
Forward Positions are considered safer areas when they are intuitively risky for Defenders to pursue Invaders into. Any deterence for a Defender spells more safety for Invaders.
For Defenders, the game is about pinning down the Invaders in a Forward Position and holding them back from the Objective. Clearing them out of the Forward Position and making them spawn back at their initial spawns is their ultimate goal. For Invaders, the game is about taking control of the Forward Position to exert their presence repeatedly through the use of Bro Spawning upon the Defenders and the Objective.
Finally, Bro Spawning has its side effects. Players have demonstrated that they can spawn their Battle Buddy through floors, walls, and electronic fences. You should consider hardening your map with Kill Boundaries, and with extra thick walls and floors near Objectives.
Summary
Bro Spawning should be intuitively available to Invaders in the Forward Position, rewarding Invaders who rely upon it, and rewarding Defenders who interfere with it.
Forward Positions should be discovered along the Invaders' natural path to the Objective, and are considered safer when risky for Defenders to pursue the Invaders back into.
Forward Positions should be areas that the Defenders can pin down Invaders until the Invader overcome the Defenders and capture their Objective.
Invasion Map should be hardened against Bro Spawning exploits.