Another Sooteater post- cut-to-fit?

Mine showed up at the shop today, just under $50 from Amazon so this weekend I'll be able to see if a BKK can be cleaned from the inside-up.
When cutting the whips, do you guys cut according to the chart, or leave it long or what?
I'll need to cut for the 8" pipe, and hope it might work for the future 6" pipe when the 13 is in place.
EDIT- After looking at this thing, I may cut the whips @ 5" from the side of the center ball. With side compression from bending the rods, I'm thinking the whips will smoosh down only so far, before whipping out again, and through a 45 or 30 degree bend, should work. Thoughts?

Mine are exaclty the diameter of my pipe and works fine.

Thanks muncybob. I don't have a straight shot up and out though, 45 deg. off-sets and elbows. The rigidity of the rods makes me think that center ball is going to ride the walls of the pipe, so the whips should be longer to compensate and be able to get to the off-side wall of the pipe.

I understand, I only have 1 90 degree turn right at the bottom on the chimney so once it gets a bit up the stack I feel better about it. Probably going to need some decent torque to spin the head. Nice thing about these tools is if you need to change the "whips" they are readily available in the garden center that sells string trimmers .