Hm, okay. If I was you, and considered IF as a must, I'd skill shield instead of STR or AGI, just like you are planning.
But how about cutting IF down to 0 and going for 21 AGI and +1 ATHL instead, or 21 STR and +1 PS? I'd personally prefer to tank less hits but be more evasive or hard-hitting.
However, don't listen to me or others unless you are uncertain about your build. Even if it looks strange or even unplayable to others, it might be just the right thing for you, maximizing both fun and performance.