It turns out that ADNS-9800 sensor has much wider view angle than I expected, so it didn't work well till I expanded the window from this:
to this size
Modified STLs were uploaded to github.
And finally I attached the bottom tray, so the keyboard body is considered finished.
Tray is just a flat plate glued to the main body.
Also the new STL can be found here: https://github.com/karol11/32xe.