The DJI ground station height mode needs to be set. There are two options: height mode and altitude mode. Previously, we were outputting AWM files in altitude mode, which gives an absolute altitude above see level at which the flight should occur. Now we are outputting the plan in height mode, which will be relative to the elevation of the takeoff point.
You don't need to touch the offset. Just make sure it is set to "height mode". The AWM file we generate handles the offset.
If you enter 80 m AGL in the Flight Planner, the flight should occur 80 meters above where it takes off.
Where is your home point set on the DJI Ground Station software? If you don't have the drone connected, it won't be able to pull the GPS signal and tell it where it is taking off. Height mode operates relative to the take off point. If you are not on-site at an elevation of 320 meters but are instead at your house preparing things at 100m, it will add the 87 m to where you currently.
I would suggest testing a layout where you are currently and have everything hooked up to pull a currently location. If you have never plugged it in, the home point defaults to the DJI factory location.