Being a student of fitting plants in, I am sure that is why I often get called a space cadet. It is surprising how high density planting can be done effectively even with plants in pots. One friend who has a pot plant forest keeps trees small and productive and his starfruit, sugar apples etc are amazing. Tatura trellising of tropicals works really well and jackfruit, mangoes and even durians can be kept small.I am not sure about lychees and haven't seem small trimmed productive trees. The old ideas about spacing are being challenged, and yes the 'dark side of the tree' can still produce.