I’ve had this issue pre-3D, but now that Moroni is 3D I thought it might have been fixed, but it wasn’t: I am not sure if it’s due to lack of satellite imagery or some other issue, but until now it’s not possible to spawn in a B788, 789 or A359 at FMCH. I know this should be possible due to numerous Ethiopian Airlines flights leaving FMCH with the aircraft mentioned above. However, there are no spawn locations available that fit even the smallest of the 3, the B788. Sadly the tracking never works on the ground at FMCH from what I could find so I can’t provide information about the exact gate that can fit those aircraft, but as you can see from the links below, it should be possible.
Hopefully, this can be fixed soon!