The great thing about standards is that there always is a document that shows how it works:
There are diffetent types of coils mentioned in it. Design A11 is widely used. It features a coil of about 43mm in diameter and about 2mm thick. The induced voltage in the secondary coil (in the N5) is proportional to the change of current in the primary coil (qi-charger). Therefore you need AC. IIRC the typical frequency is 120-175kHz. You can look it up in the specification for further details.
A change of the shape of the coil dows indeed change its behaviour as you would also change its area.
It still "works" it will still put out voltage but not the right amount to properly function.
So now how do i make a oval coil work? Would I then have to change the original ac voltage? If so that idea is scrapped. I dont have the resources this week to re invent the wheel. Maybe next week.
Then would just 2 coils be best? That way the issue with the 3 coils is avoided but it can still work for a better selection of phones tablets?