Wrong "Increased effect of soceted items" calculation

I have Abyss belt "97% Increased effect of soceted items" (Soceted items as helmet)
I put in it 2 runes for "6% reservation efficiency of Minions skills"
12+97%=23.64
But on belt there is a sign "22% reservation efficiency of Minions skills"

Why is it 22%? should be, at least 23%

I guess it count each rune separate, and it's 11.82% each, and it rounds off a number to 11 each, but it looks wrong for me... should count both (paticulary because there are TWO sockets. There are ment to put two runes in it) and rounds off a total number, and not separate

Or don't round the number at all, but leave it as it. because on 400 spirit 0,2% or 0,8% can make a difference