Mind Hunting and Astral levels

[GrudgeBringer]

Question...
I know S5 is good for late game as it is about where you want to be to protect yourself aagianst spells.

What i would like to know is...do I need to take S5 on my pretender BEFORE the game to aquire the protection, or can I take S4 and use a Cap to bring it up to 5 and will it do the same thing?

I was worried about it being like blesses, but S5 doesn't give that extra bless which made me wonder if I gould get by and spend the points elsewhere.

Thanks