Ahh, okay. Due to the angle, it looked like the inserters were taking directly from one another. Makes total sense what's going on. My mistake, thanks for the clarification!

Using LTN, I had intended to setup stack inseters to quickly fill train engines using the locomotive position encoding and then use a long arm inserter to remove any "leftover" items in the stack inserter's hand to ensure if a cargo wagon pulled into that slot the next time, the fuel wouldn't get ...