The lubed felt wad was intended to be placed between the ball and the powder. It will not be fully effective in keeping fouling soft if loaded on top of the ball. There are two reasons:
1) the compression of the wad against the ball during initial combustion and then as the pressure wave pushes the ball down the barrel against friction serves to liquify the lube material and force it out of the wad, and
2) the combustion by-products (fouling) exist behind the ball (hopefully NOT in front of it) and are in immediate contact with the lube material; thus as they are deposited along the wall of the bore they are already in a modified condition. There is no risk of the ball wiping the lube away before it can act on the fouling material.
As for the anecdotes about 'most' of the chain fires initiating from the back of the cylinder, all that reflects is that for a certain period of time a certain group of people were either more careless about their cap placement or caps/nipples went through a period of interface failure. A chain fire is not a probabilistic event - it will occur when there is an open path between a flame face and the powder. The probability becomes a part of the issue only when one is more likely to be careless about sealing one end of the cylinder over the other.
A chain fire CAN be initiated at either end. Pay attention to BOTH ends.