Amount of Breach fortress encounters

Here's a question for GGG or anyone that knows.

Are there factors that alter the amount of breach fortresses that spawn? Like does magic find help with the chance for these encounters or something?

I ask this because I am currently progressing through yellow maps and so far I have only encountered 2 fortresses in my maps. (I make sure to find the breach in every map)
A friend of mine who is at pretty much at the same progression level as me has a hard time running them, so I help him out when he gets them. He is getting fortress encounters like every 4-5 maps it seems.

So is this just really bad RNG? Or are there thing I can do to increase the chance of getting a fortress encounter?

Thanks.