Setting the values for interval without pass through being enabled will of course change the interval settings. The image will have been taken into LightBurn with its own pre-defined dpi; on being saved from any image editor. I cannot say if this pre-defined dpi is actually used to work out the interval settings when pass through is enabled.
You have correctly identified the thread where I read about the enabled pass through computing the image dpi based upon its size. I think this was the reason I felt somewhat intuitively that a more accurately sized image (350mm square instead of 677mm square) would give the software less work to do insofar as the coding required and thereby would shorten the processing time for @alalone’s image. I guess that @LightBurn would be able to answer that question more fully.
Yes, that is correct.
My understanding is that setting dpi values cannot affect the image with pass through enabled.
Yup, the overhead for processing the code cannot be escaped. I take the overhead to be computation time, excess computation time, indirect computation time, computer bandwith, computer memory and access time and any external resources which permit the software to run effectively, like the laser for example.
This is beyond my pay grade. 