We keep being told that 20-22* initial is the maximum ever reqd. Hmm. Below is by Chyr guru Steve Dulcich in MM, Sept 2013. A 318 engine with a sizeable sol lifter cam. One way of getting 28* at idle would be by using MVA.
There is a not-too-old British book (I am not at home to take a picture) and the author categorized different combustion chamber designs (many of them every version of primitive open chamber) with corresponding initial and advance timing degrees.
Now I am just a keyboard warrior as inkjunkie would say, but with different inefficiencies in the combustion chamber, the initial advance gets larger-as I understand it.