ASM SGA sizing

The query from customer DBA :

" Hello,
We plan to install X TB database .. I didn't find the rule for ASM SGA sizing.

What values i need to set for the ASM instance:
sga_max_size =
sga_target     =   ? "


I found the note 437924.1 and 
the only source in the documentation, which point to the ASM sga sizing:

• For disk groups using external redundancy, every 100 GB of space needs 1 MB of extra shared pool plus 2 MB

• For disk groups using normal redundancy, every 50 GB of space needs 1 MB of extra shared pool plus 4 MB

• For disk groups using high redundancy, every 33 GB of space needs 1 MB of extra shared pool plus 6 MB

So, for example, for 1T database with Normal redundancy customer have to yield 24-25 MB of ASM SGA.