When i was playing HQ in china town i discoverd that there was no turret where there should be. Its the one in the house where there is a roof thing where you walk over to another buliding and under that thing is a fruit stall. You get to the turret by going up stairs that bend round and there are 2 doors at the top of the stairs. Bad description but should be ok. I found that there was no turret there on HQ but was there on other modes. I guess this is because it would be too easy to defend one of the HQ places if you had the turret.
I dont know if anyone has posted anything about this but ive only just noticed
I guess it's so you can't use the turret to spray the buildings adjacent to clear any HQ's there, but that turret isn't great for actually defending the building it's in considering the angles it fires from don't cover even 50% of the buildings approaches.
I wasn't aware of this either though, nice to know.