Cruise Altitude when Filing an IFR Flight Plan In-Cockpit w/ Garmin Units

Having learned that one can bypass the World Map and file an IFR flight plan with the various WT Garmin units, I was playing around with the GNS 530 in the Cessna Skymaster.

Where does one set their desired cruise altitude with these, such that ATC doesn’t assign a max ceiling cruise altitude?

I tried entering a cruise altitude value on the GNS’ VNAV page, but that didn’t stop ATC from assigning me 14000’.

Is there a way this can be done with the various Garmin units?