Make sure these ranges are programmed in the preset itself. Easiest way is using H9 Control, where you can use the ribbon strip to ensure the range goes from -20 to -64 as you move the strip to the right.
Have you checked to make sure that the CC# you are using to map the expression/ribbon controller are not conflicting with something else? On H9 Control, if you go to PEDAL SETTING > MIDI SETTINGS > Assign MIDI CC messages to pedal functions…make sure "Set express pedal value" is set to its own CC # not already in use by something else. This is the CC# that should be programmed on the Morningstar expression input.
It's better to program expression mappings using the ribbon controller, rather than trying to send expression control to an individual parameter. This way you don't have to reprogram the Morningstar everytime you want to control an H9 parameter, but rather you can leave it to the general CC that controls expression and simply change it on the H9 Control side.