I have been having this problem for a while now. When I have a call with multiple patients and send a mixture of ALS and BLS ambulances (based on the level of the patients) my ALS ambulances are treating and transporting A and B level patients leaving the BLS to handle patients above it ability and requiring me to send an additional ambulance.
For example: I have a call with 3 B level and 2 D level patients so I send 3 BLS ambulances, 2 ALS ambulances and an EMS Chief trained and set up to transport automatically. If the ALS ambulances arrive first they will start treating a B level patient and will then transport that patient. That leaves me with two D level patients and BLS ambulances left to treat them. This forces me to come back to the call and dispatch additional ALS ambulances to handle these patients that the correct resources had already been on scene to handle.
There really should be a triage system where the highest level patients are treated first.