The synth parameters are the ones that occupy the bulk of the remote editor panel. Changes you make to synth parameters always apply to all selected zones.
The panel "only" shows the settings for the zone with edit focus.
To make adjustments to one zone, select it (which also gives it edit focus) and adjust the parameter on the front panel.
To set several zones to the same value, select them and adjust the parameter.
All zones will be set to the same value for the parameter you adjusted.