An affectionate chin is one topic that cant really be generalized. Because every one can be so different in that regards.
I have 5 chins. A mother, father, son, and two daughters. Father is affectionate as can be. Will run up to the cage for a scratch and sit there forever enjoying it. Mother and one daughter usually don't bother. But once in a while will come over for a quick scratch and attention. Son 90% of the time would avoid any attention. He will just sit their in the back (out of reach) and watch. And the second daughter is over whelmingly panicky. Almost always avoids it.
So my chins really span the entire spectrum. Over time tho, you learn how to read them. See what they want, when they want. And what they don't want, when they don't want it. Example: My girls HATE to be bothered the first hour or two after waking up.
In my case tho, i do have one small method to make my girls want some affection some times. They may not like it much themselves, but they are highly jealous of each other. If they see one girl getting attention, they will run down to try and snag it for themselves lol.