I'd just run it at 360mm all the way across & put some bigger books on the 420 side. If its anything like my place the alcoves won't be at right angles either so you will need to make a card template to check.
That would trigger me
@Tenderloin started
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I'd just run it at 360mm all the way across & put some bigger books on the 420 side.
If its anything like my place the alcoves won't be at right angles either so you will need to make
a card template to check.