1) How on earth do they know you are an Ur-Priest?

2) How do they know where to find you?

3) Having People attack you is not a disadvantage. This is D&D, someone will be attacking you. It's comparatively an advantage to know who is going to attack you, especially when your class gives you spell resistance against those people.

If your DM makes encounters that are above CR guidelines then your DM is being a jerk. If they are within CR guidelines, then you kill Paladins instead of Fighters and you still get XP.