Okay, so I've added defensive perimeter to the warehouse. I'm still experimenting with how large this perimeter should be. Currently they're just defending the room, but if the player takes the battle outside then they get clumped up at the entrance where they have a limited line of sight and are an easy target for grenades. On the other hand, if I allowed them to walk up to the sandbags, they can cover a wider area, are less clumped up, but are also more exposed to enemy snipers and sneak attacks.
I think it's generally preferable to funnel the enemies through the entrance and keep your allies inside, but I'd like to hear your opinions as well.