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.