I do know that there are very few B&Ts or rubies scanning well and finding suitable mates has been a challenge for wholecolour breeders. If more wholecolours were scanning I am sure many more would turn up; the breed desperately needs more scanned in these colours...

On head shapes -- Dr Rusbridge has addressed this a few times in Q&As and I've discussed with her before directly as well-- she definitely says size of head is not a determining factor nor is length of nose nor is size of cavalier as to preponderance of SM. What the research work in this article is showing is that internal area for the skull is a determining factor but this may not correlate at all to outer shape, it is an internal skull measurement for volume. A very experienced person who has looked at hundreds of cavalier heads and MRI scans and skull xrays could likely pick out a likely 'good' skull externally but this would be very hard without shaving the dog! I know one researcher has said people misjudge heads all the time because of the position of ears or the way the head is being held and see shapes the skull doesn't have.

However as miniaturising dogs does seem to be one factor in the appearance of SM it would seem that simply being a toy breed is an issue.