Reaction ability activation%?

I did experiments to verify wich stats or other things are related to the probability of activation for reaction skills
My first tought was to try with different lv units with different parameters
I also tried with different elements units and etc
For what i discovered till now it seems that only the bravery of the unit and the lv of the reaction ability are related to the probability to activate the reaction skill

Also can someone extrapolate a formula based on this data?

lv 2 skill brave 91 = 5%
lv 3 skill brave 91 = 5%
lv 4 skill brave 91 = 5%
lv 5 skill brave 91 = 6%
lv 10 skill brave 97 = 13%
lv 12 skill brave 97 = 14%