I've noted your comments. If you do not employ tilt, shift, rise, fall and swing and whatnot in the larger format, then perhaps you should not be using that format. You said, "I understand what to do", but in the next breath, "but I'm never sure if it's right,". Well truth be told, there is no right or wrong. Nobody is creeping up behind you with a cat o' nine tails to whip you onto the straight and narrow of compliance to some obscure, unpublished rule that is right and that must be followed. You are participating in an experimental and quite variable branch of specialist photography. What there is to learn is done by actively using and employing the functions available to you in the larger format. There are very few published scientific texts to propel you along, and Merklinger's is one of the best, but you do not need to take all that on board to come away with a beautiful image. It does require refined skill and precision that you learn through experience, and much of the adjustment is by visually following the plane(s) as movement is introduced. That's the way it is. It is not relevant to dissect Merklinger's voluminous writing on the Scheimpflug Principles. Though informative, all that text has the capacity to dent the confidence of people who are not extrapolating writing into active practice, or feel intimidated. Depth of field, focus plane and subject alignment are all learnt behind the camera.
What do you mean by "Situations where there is a lot of depth and multiple planes, and tilts and swings cannot be used"? Why can't the movement(s) be used? If you are using an ultra-wide angle lens you will generally not have to introduce tilt to extend depth of field. Shift/rise/swing can be employed for perspective correction and elevating/reducing the scene.
When I photographed a waterfall in 2003, previous research of the subject alerted me that it was not facing the camera in an ideal plane, nor could I move the camera closer to it. Using tilt, I "turned around" the waterfall, in doing so, creating a 'peg' of near and far focus (extensible depth of field) while choosing to leave the periphery (of unsharp/out of focus) surroundings 'as is'. Depth of field and by association, focus, was completed visually.
The depth of your enquiry is troubling because it introduces a huge and potentially complex layer into the photographic practice that is not only distracting, but unwarranted. Will you ever get the picture done if you are considering so many principles, functions, calculations, permutations, measurements, conversions etc? To learn all about the how, where and wherefore, load the film holders up and go out and shoot, applying movements as you desire (and keeping notes of what you are doing as a valuable learning aid). Then come back and show us the beautiful pictures you created. Stuff the mathematics and diagrams.