I'm going to be replacing my leaking water main valve, and I'd like to use a sharkbite fitting. I notice the slip joint ball valves (part# 24735LF) do not have the interior white nylon collar (see first picture) that the straight ball valve does (part # 22222-0000LF). What is the purpose of the nylon collars? Don't these collars restrict flow because they decrease the interior diameter of the pipe? And since the nylon collars don't fit flush against the interior of a copper pipe (they seem to flop around inside copper pipe - see second picture), doesn't this lead to more turbulent flow at the entrance to the valve? I'm wondering if I would get better water flow through the slip joint because the interior diameter is wider and the path straighter without that nylon collar? Or does it really not make a difference?