Sure I get it.
muling the my.y by that factor will reduce it towards 0 every frame regardless of the sign of my.y pos.
it is not regulated by time_step.

The basic logic is a mul by .9 reduces the my value by 10% and to increase the shift rate you decrease the decimal value.
So then a mul by .75 will decrease the my.y pos by 25% per loop.

I understand, but does the OP understand. We both present a logic design to achieve the same effect. But if the OP doesn't see the logic then they can never use that logic to create variation for similar effects.