This had never occurred to me (despite passing my Intertype composition test as a student). The matrices in the magazine on a Linotype machine are ordered from left to right by English letter frequency (etaoinshrdlu…), as is the keyboard. So matrices from a cast line that are returning to the magazine drop from the distributor bar in letter-frequency order, meaning that the matrices most likely to be called next by the operator are most quickly replenished in the magazine.

See Circuitous Root.