The problem is that what to do with alert is missing. so it should be something like "At the beginning of every round after the first roll a d6+Alertness for Reinforcements. On a result of 4+, enemy Reinforcements arrive."
As for my unsolicited suggestion. maybe make it a 5+ but with an additional +1 every 2 or 3 rounds.
Also i found another inconsistency, on Kill Them All says "Reinforcements appear on results of 5-6, instead of 6.
" could be changed to something like "add 1 to the Reinforcement roll"