The head of a fly line consists of the front taper, belly, and rear taper combined. Usually in most salt water weight forward fly lines, the head stores enough grams of weight to load the rod for a quick presentation.
When casting, to take full advantage of the full amount of weight needed to load your rod, you will need to carry the entire amount of line in the head outside the rod tip. Then and only then will you feel the rod load completely and deeply.
Fly line manufactures build lines with the correct amount of grams of weight dispersed throughout each head in each wt line to appropriately load each rd of equal wt. This helps to keep all rods and lines in balance so any 8wt line should load any 8wt rod.
I am keeping it all fresh. Stay tuned, I will talk more on this in my next post.