When determining correct chain size, one common technique is to install the chain (without passing it through any derailleur) onto the largest front and rear sprockets. Then, determine the shortest length that the chain could be cut to, and then add 1 complete link to that length. One complete link corresponds to one inner and one outer pair, which corresponds to 1 inches.
I have noticed that in recent times, some resources recommend adding 2 links (2 inches) instead of only 1, specifically when the bicycle is set up with a single chainring in the front. This seems to be a "tribal knowledge" practice, but fairly common in my area.
Is there any evidence or data to support this practice of adding an additional link to 1X systems, and are any major component manufacturers recommending the practice?
See for example :