I have no idea how to do it myself, but Creeper keeps pulling it off on nuclear. I swear there is a restrict brush in place, so that most can't do it (hence only two turrets were present last round - Candles), but there's clearly a workaround for it.
I tested it and reported it somewhere else. It actually works a little different to what you are saying. But you can't physically be outside the brush in my situation, it wraps all around the base.
Unless it calculates your movement funny and predicts you'll go lower than the floor brush, and then you can really quickly place it before the server realises what's up and puts you on the ground, then it's *still* not it. However, that would need testing and if it's the case, fixing. Also, I lowered the restrict brush to go quite far under the floor, next time Creeper plays we may see if it's fixed :p
Your map kind of just has bug. Last time I played it. You didn't need to do anything to place turrets. It just let you. But dying and going back to the same spot it would be restricted. Kind of like restrict brush was randomly not there. The exploits that allow building in restricted areas on other maps wasn't required. Might want to check if maybe one of the faces in the brush is missing or if maybe there are spots that it's not covering. Also why restrict turrets ? Instead of restricting turrets just add more cover in maps.
I checked, double-checked, and triple-checked the brushes. This should not happen, the brush is literally right there and working as intended. Sometimes. Also I restricted turrets because they would block the vehicle path for way too long.
This is happening because you have a emp_eng_restrict inside another emp_eng_restrict brush. When you leave the inner brush it will not reapply the settings from the outer brush, instead it will return to the default restriction settings for that map. This can also cause issues with overlapping brushes, and even if brushes are very close to each other could result in touching one brush without untouching another because of the size of the player. Basically If you touch one brush without untouching another, it forgets about the first brush until you exit it and reenter. I'm just putting this here for reference atm.
