Mine are at grate level for I guess the main reasons already mentioned. I want to force my smoke to linger a bit rather than make a straight line exit. The path of the smoke also represents the path of the heat (in my mind's eye) so my thoughts are to get that smoke rolling and disperse the heat in the process. What would be cool is for someone with a top flush set up to run some therm readings with the current rig. Now put an extention (rolled up piece of light aluminum sheeting) down into the smoker to lowest grate level and re test those therm numbers. Might be there is no benefit either way.
If it can't be smoked .... try frying it. It that don't work, it's probably best just left alone