No real time for a lengthy reply just now as I am busy with the relocation of home and business some 200 miles away. Small matter of 100 meters squared of workshop and parts to pack and move.
In short, the reason for the minimum squish I stated is due to mechanical and thermal movement, which will depend on many things. Parameters can only be observed in the real world and any figures given are "safe known" figures that I can recommend from experience. Long term mechanical contact of the piston and head will result in either piston or rod component failure. On one of my 350 race engines with a 40 degree squish, once below 20 thou, you will get piston to head contact. In reality that 20 thou is more like 12 thou vertical distance. The piston will expand when hot both in length and diameter (both affect the squish) the rod will stretch etc etc, and that 12 thou will disappear. Then again a road engine will not be under the same circumstances so you "may" get away with less, but why risk it?
Another problem is that if checked properly many squish bands do not line up concentrically with the bore/piston and can mean a very uneven squish. Measurements taken with lead wire (solder) without any piston centralisation will lead to false readings. This is due to the piston being very slack in the bore at the top when cold and there will be a tendency for the piston to just more off centre and the lead wire readings will be more an average than real. When hot the piston expands and piston will run more centrally. Anyone who has worked on many Ducati singles and not observed any out of concentricity, is not looking very hard!
Squishes used on other manufacturers engines are not necessarily relevant to Ducati singles as the design and parameters will vary.
A good working squish will help combustion and it is noticeable that an engine with a efficient squish will need less ignition advance.
The reason I do not like any significant "converging" squish is I don't think having potential trapped unburnt mixture is a good idea, as you are possibly inviting detonation. I have been led to believe that larger wide squishes 60 thou plus can also lead to detonation on performance engines as well.
I'm no university theoretical engineer, more a practical observant one, so I can't give all the science behind what I know. On the other hand, many learned theorists can't build fast reliable race engines so I am happy enough
Regards Nigel