Unscientifically determined, but the mini displays approach plates the same size as a real, paper one. I use a RAM mount suctioned to the window. Works great in a 172 if you mount it on the little side window, where it does not block too much of your view.
RE: the A20, yeah theyāre pricey, but worth it. I canāt fly with anything else now. Periodically, Bose will run deals. I got mine on a $90/month for 10 months, no interest financing.