look in the FMC under the PMDG SETUP > OPTIONS > SIMULATION.
on one of the pages is the settings for:
CTL COLUMN NULL ZONE
CTL WHEEL NULL ZONE
which are the dead-zones % for the FBW flight path hold mode
(note the are not stick dead zones but explicit FBW dead zones, so if you have zero dead zone set on your stick a setting of 10% for each of the above wont change your actual stick feel, it will just change the explicit FBW flight path hold mode dead zone).
if you find the PMDG manual for the 777-300ER and look in the section:
Fly By Wire (it’s not an Airbus!)
it will give more info, of I recall the link to the can be found on the forum in the top right margin “PMDG 777 Documentation”