Correct, the cab is a miniature building both inside and outside, so adheres to the same acoustical physics. Note that peaks/nulls can't be cancelled out, only averaged out by shifting them to many more smaller amplitude ones that will in turn decay away more rapidly due to being lower in energy.

Inside the cab can be damped of course, but always best to keep it to a minimum IME, so while using an offset is primarily for the exterior, you 'kill two birds with one stone'.

Making as many different path-lengths to the various boundaries as practical does this. A circle with a sound source dead center will radiate in a virtually infinite number of peaks/nulls all at the same frequencies, so with a large baffle this can be quite audible as they comb filter with the driver's output.

GM