Question regarding NPCZone areas

So, I was wondering if there was a trick to make this simplier without creating multiple areas.
I have the NPC zone volume, spawn volume, and manager all together. Working (Well for the most part, min dinos set to 500 and it only spawns 136, dunno why)
Is there a trick to have 1 manager control multiple spawn volumes, or Do i need to create individual manager/zone/spawn groups? Ive tried with 1 zone volume, 1 manager and numerous spawn volumes and it just doesnt do anything different.