I'm not sure I follow? your not going to use the sprayball to output wort from the rims are you? that would require high flow and certianly result in channeling if it even works, also it would oxidize the wort pretty bad which is no longer a popular thing... sparge arms that sprinkle onto grainbed are for fly sparging not for recirculation or even batch sparging.. zero benefit. disadvantages actually although the folks selling the fancey sparge arms wont tell you that. I use a regular piece of silicone hose set to deposit the wort back onto the top of the grainbed.It could have been channeling, at the time my rims output is/was just the tube back into the cooler mash-tun, I got a CIP ball few days ago to hopefully improve that. I don't (yet) fly-sparge, it's still batch effectively, but could have caused some channeling with the output from RIMS, will watch my output valve.
I use the hose as you describe. this creates a swirling level of liquid at all times on top of the grain bed.I guess then do you avoid channeling just by pointing the hose at the side wall of the tun and/or the flow rate being super slow. I guess I figured the CIP ball would help break up the flow thus stopping any potential channeling.