Monthly alpha - semiarid region

Hi guys.

The template provides the option to use monthly alpha values. Indicates this procedure mainly for places with a highly seasonal climate.
My study area is a semiarid region of Brazil, with high seasonal precipitation.

For these locations the model suggests that the alpha should be set to the antecedent monthly precipitation values, relative to the total precipitation: Pm-1/Pannual.

I did this procedure :

Is that correct? Can you help me?