iPV shade derating appears to be incorrect

If the shade derating % looks the same regardless of the obstructions, you may not be “tracing” the skyline accurately. When you do a scan you must keep the crosshair sight on the edge of the skyline obstruction as you turn, e.g. if you have a tree you need to trace out the upper edge of the tree with the crosshairs as you turn. The app is recording the phone tilt as you turn and using these readings  to determine the obstruction profile. It is not taking pictures.