I'm still relatively new to AZ, but I thought I was informed that Photo Enforcement vans need signs at 0.5mi and at 300ft, just like the permanent cameras.
But I'm noticing lately that they are putting the first sign way further than 0.5mi, like at 1mi and once, 1.3mi (nearly triple the distance). It seems like they are trying to fool people into slowing down for longer, or into forgetting that the camera is waiting for them.
In fact, I saw one where the sign was before an offramp, and the van was just as traffic merged. Not only was this distance nearly a mile, but the merging traffic (who are getting up to speed and possibly speeding from downhill onramps) purposely don't get the 0.5mi warning.