SR5 Centering Dice Limit Options

[coolgrafix]

Started playing a mage in SR5 recently starting with more karma and credit than normal.

First session we played I was told that my centering dice (initiate grade + centering focus rating) could not exceed my magic attribute.

So, this meant that my rating 6 centering focus would only act as a rating 4 centering focus, since:

Initiate Grade: 2
Centering Focus: 6
Total: 8, exceeds Magic attribute by 2, thus nerfed to 6 total

I have a memory of finding this limitation in the book during the game session and believing it to be correct. But now I can find hide nor hair of such a restriction. Can someone point me to a page?

Thanks,
Brad