The Myers spoil board was a good design but Mr Myers did not take into account several things. First if you make the spoil board the maximum cutting dimensions you cannot surface the whole thing leading to ridges at the back and/or both sides. Secondly his files from his sites were designed in an older version of CC so sometimes the files do not work properly on newer versions of CC. It is usually just remaking the tool paths but they may work as saved from his sites.
I have posted this before for the Shapeoko 3 machines but it is applicable to the newer 4 and 4 Pro models if you want a supplemental spoil board on top of your hybrid table.
Enjoy spoilboard_considerations.pdf (1.3 MB)
Please reply if you think it was helpful.
On a Shapeoko 3 XXL the travel dimensions are something like 33x33 but part of that 33 is hanging off the front so for a spoil board you want it completely supported and not hanging off the front edge.