I've never had a 90 degree angle sunshade work. My sunlit face is always reflected back at me. Best to use a sunshade that has a back to roof angle of somewhere around 60-75 degrees (depending on the depth of the shade) so any reflection you see will be the dark underside of the shade -- basically no reflection at all.
I saw a YouTube video where the guy suggested a cutting out a piece of cardboard and bending the bottom to 90 degrees and then sticking it in the mount that you are using between the top edge and the tablet.
I had a Kellogg cereal box that was empty so I have Tony the Tiger blocking the sun for me.
Inexpensive and a cheap way to see how you like having a mount on your controller.