There is only rather poor pic at the moment, it is still unfinished but seem to be working well even how it is:
It has more or less constant arc, sides are taken inwards bit more aggressively than top.
I did measure from top that in 50cm distance there is 5cm drop, sides are maybe around 8cm which might be bit too much, but I was not able to make them any lesser angle while maintaining top side angle.
It is made from 0.5mm metal and seem to be very solid without any supports, however I plan to add some bracing which might get it shaped bit better too.
I'm bit surprised that there is so much of improvement at this stage already, but despite my repeated attempts in measuring, I have not been able to measure any worse results, so it looks like that thing is working so well.
edit: Oh yes, there is one pic from behind when I was still planning it, decided against this shape in pic and made it to be more of an arc, but sizes and general angles are pretty much same:
