Top cover for F450 frame CAD remix

I accidently bumped into this topic and the drone enclosure catched my eye.
https://www.thingiverse.com/groups/anet-a8-prusa-i3/forums/general/topic:34474

Not only the .stl had problems, the model itself was well designed, so I copied that in my spare time as a part of cad practice.

The bottom part was great with unseen details.(except for those corner chamfers' value) But the top part was not good with uneven thickness.
As a solution, I kept the inner slope angle and height, then completed with constant 2.5mm thick shell from gradient extruded part.(used arctan function for gradient extrude)

Designed with Onshape, reference .step converted with FreeCAD.
https://cad.onshape.com/documents/296a06b97c90b2746ef48d89/w/5fe611ed0a8eb098a81e47bb/e/14b2f5aa7fffdb843f26c0ea