So, using a 4x5, I'm shooting a 150mm lens, 8x is 1200mm or 47", let's say closer than 4 feet. If I'm shooting a 75mm, 600mm or closer than 2 feet. A 210mm would be 1680mm or closer than 5 1/2 feet. a 300mm would be 2400mm or closer than 8 feet.
So how do you keep track when using these many lenses?
Here is the secret:
1) don't use so many lenses for close work; and
2) if you do use lots of lenses for close work, remember that the *"tipping point" will image essentially the same size of subject, no matter what lens you are using.
This just means that you need to be able to see when you are close enough for it to matter. And to recognize the size of a full frame subject when you are close enough for it to matter.
That size may be something like the size of a typical shoulders and head portrait frame, or whatever else resonates for you.
That is the visual "flag" that raises in your consciousness when you are working with a camera where bellows extension exposure issues may arise.
With some practice, you will easily see when you need to deal with the issue. After that, it is just a question of doing the calculations.
Exactly the same issues arise with my Mamiya C330 and with my Mamiya RB67 when I had it. Those cameras though have features that help with the issue.
*"tipping point" = the minimum subject to camera distance where bellows extension effects on exposure become meaningful.