Waypoint altitudes

So I went out to use Tower for the first time today. I’ve previously used droidplanner v1, but it was buggy and unfinished so I was eager to try v3 for creating waypoint missions in the field.

In principle it works great except for the way altitudes appear to be handled. For some reason I could not set a waypoint altitude greater than 200m and since it all seems to be based on ASL and my home altitude is just over 180m it was unusable.

Have I missed something? Is there anyway to make waypoint altitudes relative to home altitude, which in my mind seems to make more sense?