Telvis, it can be very confusing if you are just getting into this degree of tuning. When I was trying to "tune my way" out of detonation last year, guys like Rapid Robert and Cab Burge were right there to help. Sometimes I was overwhelmed with info to the point that I was drowning in all the jargon!
My take: Some engines like more timing than others. The only way to know what yours needs is by trying different settings. Some just set the initial timing, see what the total turns out to be and leave it at that. I've learned that there is SO much more to distributor tuning than that. See, it isn't just the amount of advance that the distributor delivers but how fast that all of the advance gomes in. The rate of advance is what takes time to tune. There are weights inside that extend outward as RPMs increase. They determine how much additional timing is added in addition to the initial timing. The movement of the weights is limited by small springs. The stiffer the spring, the slower the rate of advance. The heavier the weights, the faster the rate of advance. There is much more to it but this was a simple description.