Upland mangos sweeter than lowland mangos?

Mangos are ready for harvest usually after 120 days from the 1st day of spraying flower inducer using potassium nitrate (KNO3).

Our experience, and corroborated by other mango growers and sprayers, is that if your mango trees are in the lowlands, you need 120 days before harvest But if your mango trees are in the midlands to uplands, we can harvest 115 days, sometimes 112 days. Why? The fruits mature faster and start falling to the ground before 120 days, resulting in a potentially big crop loss.

I notice, and again corroborated by other people, that upland mangos are sweeter than lowland mangos. I have personally tasted mango fruits on the same barangay or village. One in the lowlands, after 120 days harvest; the other in the midlands (ours), 114 days. Result? Ours in the midlands are a lot sweeter than those in the former. Even other people who have tasted the same set of mangos said the same thing.

Still don't know the exact explanation why this is so...