I am not sure that it is different presentations.
My feeling is that it is the cooler water right now and the fish are looking for smaller insects, ect that the PTN represents.
Later the water is warmer and the fish are more active and will go more the the other flies with harder hits.
As they fish are more active as the water warms I think there is more competion for the food so the fish hit harder as they don't take as uch time to look at the fly.

Rick