Controlling roller shutters with Openhab Alexa skill - percentage


I want to be able to close / open my roller shutters by specifying percentage step:

Alexa open living room shutters by 10%.

Basically it is working, almost :-). The problem is that the value I get from the skill is not the step value (10%) but position in percentage. meaning, if the shutters were 40% open, I will get 50%. This is an issue for me as I can only work with step values as I don’t have control by position.

I assume that the skill gets the current position before sending the new one.

Is there a way to get only the step value? probably I can overcome it in a rule with a patch but before I do it, maybe I am missing something here.

I use DIMMER as the item for Alexa.