Hi Jan,
yes, on application side you have to decide if you extract a value as info or control data (2 different extraction functions). On EM side you then have create corresponding parameters as well. If you extract as info data you have to create an info parameter, if you extract as control data you can either use control parameter (stored as name-value pair in generic table /SAPTRX/EH_CNTRL) or as system parameter in custom table (some more customizing needed).
Best regards, Daniel