I have land in India (the tropics), in the hills, on a slope from 6800 feet - 5200 ft altitude (roughly). At that lowest point there's a stream of about 10-15m across. Generally my entire land is a very sunny area, high UV radiation, though not hot like the tropical plains-- it's more Mediterranean perhaps, or maybe like some of the Andean highlands, plus a relatively less intense monsoon than the surrounding region (it rarely crosses 28C even in summer, usually hangs around 20-25C during the day. In Winter, it drops to a minimum of 7C, and hangs around 13-19C during the day. I don't know how many hours those min-max numbers are sustained over).
My question is: if I were to try to grow Lavender, Tomatoes or other european herbs and plants (our weather/soil in a general sense seems suited to many of these).. plants that are defined as needing "full sun", do I need to reduce the hours usually suggested because of the tropical sunlight and high UV? If yes, is there a way to calculate that or perhaps some sort of thumbrule?
EDIT: When I say tomatoes, I mean San Marzano, Roma etc.