Period lot size with planning calendar

Hello PP colleagues !

I have been spending a lot time trying to customize a scenario a planning calendar with calculation rule  weekdays and it doesn't work. I don´t know what I 'm doing bad. 

I need that the MRP create planned order at the begin of each periods in planning calendar (each three days), but this create planned order as the begin of each week.

The planning calendar is as follow :

The  lot size procedure is as follow :

And when I run MD41 by material, the results are  :

Please , I need your help, because I don´t understand how to customize this in order to allow to work as I need.

Thanks a lot for all your comments.

Regards

Vero