REP's can know very little. They are the people representing the companies to try to sell more stuff to the shops.
Think for yourself.
Say you have a given tube, it's diameter and it's length.
Now increase it's diameter. You need to thin the wall thickness, of course. It's stiffer.
Now decrease the diameter. You would need to increase it's wall thickness, to keep the same weight. Now it's got slower REFLEX.