My experiance is that you can get a lower idle with the idle bar plug. I see no differance in performance if you compare the idle bar plug to the equavlent non idle bar plug, the Fox RC standard and idle bar are the same plug. The engine will perform the same on either plug. If you are getting better performance with the 1L over the K&B idle bar then there must be some differance in the heat range of the plug. I recall that the K&B idle bar plug is slightly cooler, but not sure. There is no need for a "straight shot" as the ignition occures with any molecule in direct or near contact with the element and the flame will propagate through the sides of the idle bar just fine.

I recall that the TST ported ST .60 Blue Head needed an idle bar plug worse than the baffled ST .60 Blue Head.