Query Regarding Ramp Effect and End Date in Regression

[VabelGit]

Dear Jdemetra Team

I need to create a ramp effect between the dates (YYYY-MM-DD) 2021-07-01 and 2021-10-01 (each observation is taken the first day of moving - month) and as the picture show,

However, in order to achieve these months as a ramp in the regression, I had to set up the ramp from 2020-08-01 (one period forward) to 2020-10-01.

I want to know why is needed to set up one period forward as the initial date, since this seems not to be needed on the final date, also , since the ramp extends up to the observation of October 2020, should the ramp's end date be set to October 1, 2020, or October 31, 2020?

Thanks