Incremental Refresh: Should RANGESTART also fold?

Hi d_gosbell 
thanks for your input.
I also expected the parameters to filter into the query. And I DID define them with the case-sensitive spelling as you showed and as per the Documentation. The all caps was just to make them spring out - but in hind-sight might have caused more confusion.

Double-checking the documentation once more I DID find an interesting hint, which actually let me find the solution to the riddle.
The date field I wanted to use for the range parameters is on the DB side a DateTimeZone rather than the DateTime mandatory for the range parameters. Since I could not have the range parameters as DateTimeZone, I upon import converted the CREATE_DATE field from DateTimeZone to DateTime. Now the filtering was possible. But only on the Power BI side, not the server side.
So I now use the DateTime range parameters and convert them within the filter step into the CREATE_DATE's DateTimeZone format (rather than converting the field).

Now they fold correctly to the source.

THANKS FOR YOUR HELP d_gosbell !
Many times - even if not presented to you on a silver plate - such interactions help you find the solution yourself.
Have a nice weekend!