No problem.
Basically it works like GZ, but with the added level of wherever your spotted only insta-alerting this smaller area. if you're spotted and miss your 1-2 second window to neutralise the enemy then every guard in the area is insta-alerted. And a guard with a radio will call HQ to alert the whole region.
But 'area' is not always the same size or shape.
If you're spotted in a town of 15 buildings and 9 guards, then one shout will insta-alert all of them (just like in GZ.) However, they will have to radio out to other bases to alert the region and get backup.
If you're spotted out on a road in the middle of nowhere, by two guys walking along, then only those two guards insta-alert. There are no other guards nearby to get alerted, too. The alert sounds don't happen, and it's actually only these two guys who are alerted to your presence. Nearby bases etc. will have no idea, until one of those guys radio in. So if guards are isolated enough, getting spotted isn't a biggie as long as you take them out before they finish their radio message.
Basically it's insta-alert by proximity. Only nearby guards get insta-alerted, and this is just like GZ. But unlike GZ, guards in further away bases/outposts won't be alerted until someone radios up to them.