Collaring and slab bashing

Hi all, I was facinated to read all the stuff about throwing and collaring as I've been trying to throw a number of closed forms recently. I find that when 'Knuckling' up if the finger suporting on the inside is slightly lower than the knuckle (or finger)on the outside, that the clay has little choice but to go inward. I use the usual three digit triangle thing for collaring but, so far, when getting close to closing the top with a kind of gentle pinch I get a tiny dimple on one side of the pot; I have to say I make this more difficult for myself as the shoulders of the pots are quite broad and the dome formed in closing quite low. The stuff on slab slapping was interesting as well. I was taught to beat the clay out with a rolling pin held level and only to roll towards the end of the process. Like the slapping, beating puts the clay in compression (it prefers this to being stretched by rolling, and it does remember, I should think slapping has a similar effect. If anyone can tell me how to avoid the dimple I would be most grateful. Cheers, Andy