The main reason for tangle is due to how you are casting the team of flies.
Other reasons may be related to rod action. For wet fly fishing a mid flex slow action is the best bet. This allows for a wider slower casting loop. Distance is not for the most part required.
It is a presentation deal more than anything else.
Next reason is using large of heavyweight hooks for the diameter of mono used.
Makes no difference if the flies are tied to the upper or lower tag. The difference is the lower tag is stronger than the upper as the knot is not being stressed when a fish is hooked.
I determine the diameter of the line used related to hook size of flies, in most cases the breaking strain is not the issue.
I can deal with big fish on 6 or 7x, but it would be foolish to fish 3 flies on 7x, that is asking for trouble.
Davy.