Thank you for your response Romullus, but I must say I disagree...
it is crucially important to support frontal mapping on the corona sky. Besides, it is listed in the dropdown options in the corona sky object, so it should work as expected.
As frontal background, it works just fine, it is just as seperate reflection that it is incorrect for reflections, if you see the results or explore the file, you should agree the result is not expected
Of course I wish I had availability for spherical 360° drone shots, it would simplify the entire project, but at this moment I don't have them or the extra budget.
I also thought about the plane as reflection, but it is pretty difficult to cover all reflective materials, because they are in different angles to the camera. The plane would be too large and thus cast unrealistic large scaled reflection
and also, I have 40 cameras for stills, so it would be a huge work to adapt the planes, and find the right size for every camera...