I think you can not get parameters for the control format when you use in a report definition. Even if you use some OOTB control with parameters that will not be available with parameters when used in the Report Definition control format.
String key = (String)itr.next(); //Key has all the parameter page keys
So, you should push the property you want to pass as a parameter to be made available in parameter page so that you can read the value in the custom control. Or you can read the any property on any page and pass in the custom control code using pega public api
I tried with index, and in my case, index is a predefined parameter page property, so I see the value is coming up when running the report definition.