I use a simple contact sensor with an RF transmitter to fire a relay output on the receiver up to 40' away. This receiver is enclosed in a steel box with little or no air gaps, usually a NEMA 4. It seems to work ok with an antenna wire run out through a small hole in the box. I've been looking for an alternate transceiver, and have tested 3 (completely different vendors/models).
The original used 318MHz, and will barely if at all communicate w/o an antenna. Same for the one that uses 915MHz. The one using 433MHz works as if the box isn't there, up to over 100'.

I understand there are a lot of factors to consider which frequencies will penetrate which materials under certain conditions, but is it just dumb luck that this 433MHz transceiver blows the others away on distance? The receiver doesn't even have an antenna wired into it. I have a SS enclosure on my desk that I put the receiver in, and walked various distances (same path) away from it inside the building for my test. In real life, the transmitter will be outdoors mounted to metal moving between 10-40' away from the receiver, mounted inside said metal enclosure. I would like to understand if the frequency has something to do with it, and why. I don't have access to additional models by the other manufacturers using 433MHz, so I need to understand why the one works so much better. Incidentally, it is the smallest, lightest, cheapest one of the 3.