I lived in Miami when UA had strong presence at MIA.

At its peak, UA had the following domestic flights out of MIA:

3X IAD (777, 757, 737)
1X SFO (777)
2X LAX (777 320)
1X DCA (727)
1X LGA (727 or 737)
1X JFK (763)
1X EWR (727 or 737)
1X ATL (727 or 737)
3X ORD (777, 737, 20)
1X MCO (757)
3X DEN (777, 757, 737/320)

The 777, 767 and 757 from the domestic flights would then used for flights on the Latin America routes in the evening.