I see your theory using muddy water and a board if we are speaking of fluid hitting a solid object, can't see similarities from your example in relation to constant control flow of hot forced pressured air little to no resistance inside a controlled area (a pipe) having trouble seeing back flow occurring... nope! The exhaust converter is like a handful of soda straws inside a pipe (no resistance) hot exhaust goes through converter made of platinum metal that is heated several times hotter then the pipe it houses them burning off hydrocarbons & other air polluting emissions before it's released into our atmosphere. No backpressure, no backflow, and no crosstalk.
Unless the engine starts in reverse, (Harleys can sometimes do), but not in this case.

Closer related to your theory, how about a pebble inside a garden hose (a constant controlled pressurized environment), the water will hit the pebble causing resistance but water continues to go over and around pebble in one direction only, again no back flow.

B Bop

 

1 Canuck, I never said that crosstalk actually does occur on Harleys. B Bop was just asking how it was possible.

BBop, you asked for a layman's explanation so that's what you got. Now if you would like to go into fluid flow dynamics and more importantly how fluid dynamics differs from air flow dynamics. Well, that won't be a layman's explanation.

And for the record I put a '09 headpipe on my '12 Limited which has the O2 sensors up by the heads. SO if crosstalk does exist on Harleys it wasn't happening on mine.

Additionally if you look a little further into how often and under what throttle conditions the O2 sensors are actually sampling the air, you would stop worrying about it all together. (Hint...it's almost negligible)

 

If the cat offers no resistance to flow, then why is it that a 2.5" or 3" baffle can be run in mufflers without hurting torque. But when the cat is removed with the same mufflers you need to drop down in baffle size. This resistance continues to increase as the milage goes up due to carbon build-up.

 

Damn this was one of the most entertaining threads I've read in a while !