Well, a few questions:

1)I always thought that the things "happen" on the 1st plane only, but you can see how things "look really" on the other planes. How is it actually?

2)In AoS Bart says that "he would look like blackbird on ALL seven planes". But on the 7th plane all things look like how they are really looking. So how can he look like blackbird even on 7th plane?

3)Can a spirit get invisible on the first 4 planes when summoned, meaning the magician couldn´t see it?

4)Can magicians have the resistance to magic attacks?

Thanks a lot and sorry for wasting your time.

2) He said that at the distance he was from the guards, he would look like a blackbird on all planes. Obviously, it only works in close quaters.
3) Sure, they wouldn't be able to see it, but they still could hear, smell, and sense it.
4)Those people are born, not made, so if one those was chosen to be a magician, sure.

3)I actually meant the spirit won´t make any smell etc. so the magician would think he failed the summoning and will go out of the pentacle.

Thanks for answers.

It wouldn't work. The magician would just order the spirit to show itself, game over.