David Vizard tested 10,000 cam combinations for Crane cams. That testing, plus his decades of cam dyno testing showed patterns evolve. One was his '128 rule' [ look it up on the web ] & the other is a computerised cam program. The 128 rule is for determining LSA for parallel valve heads in general & works for CRs of between 9.5 -11:1. For splayed valve heads like the BBC, 131.5 is used instead of 128. Correction factors are used for higher CRs & blowers etc.
Until I can find someone who has tested more cams than DV [ no luck yet!] I have been & will continue to follow his advice.
In his Chev books, he says if you want a smoother idle/more low end, you do NOT widen the LSA, you reduce the duration. Yes, might be in a Chev book, but a Chev is just an air pump...like a Ford or Mopar.