I'm not the OP I'm helping him too lol...by what I said I mean it starts at the tips and covers the surface area of the leaves moving INWARD from the tip. usually burns on the inside of the leaves seperate from the tip is another problem.
Nutrients pack into the leaves from the stem, which forces the older nutes to build up near the ENDS or tips of the plant, I've never seen nute burn on the sides of the blades unless its connected to the tip burn.