I find it ideal to TL from the middle as long as there is enough experience on the trip. It allows you to see every one. Which is exactly what you need, to do your job, be the "big picture" person when there are issues.
Most TL's prefer running first with multiple boats and 15-30 customers, for a very good reason the least amount of work. When you hit camp you just untie the heavy grill box, heavy coolers, water jugs etc. and allow the customers to unload everything up to camp. Then as planed in advanced when all the heavy stuff is unloaded the last cargo boat with the first aid kit and repair kit and customers bags shows up. If they get their bags first, they will scatter into the wind never to be seen again, till dinner. Then with all the heavy work done all the guides can have a cold one or what ever.On a commercial trip with multiple boats, where in the order of boats is the best position for the trip leader?