Here's what I got in 10 seconds of research... There is no formula to calculate a puckline. Some shops move the puckline/runline independently from the moneyline if there is significant money on one side of the puckline. For example
Team Alfredson -120 vs Team Charra +100
Team Alfredson -1.5 is +190 (note: all pucklines are roughly a 100 change in the line, -120 to +190 here)
but... If I placed a $100,000,000 wager on Team Alfredson -1.5, the book could move the Team Alfredson puckline to +180 (or whatever) while keeping the moneyline at -120. There is no "formula" for the puckline, it changes with action. Just like a spread. Alternative pucklines are a NHL prop that isn't offered at all books and I know little/nothing about how they work. Never bet one in my life.
Luck is what happens when preparation meets opportunity.