You want to install as high as you can, you just have to check your installation instructions how much clearance you need for the above grid. Most tiles require 3" overhead clearance this way you don't sacrifice to much headroom, some tiles require 4". Also check how much you need if you will be using 4' x 2' or 2' X 2' lights, usually we measure the height of the light and add 2" for overhead clearance.

If you plan on using recessed lights and you want your lights to be dead center on the tile, most likely you have to settle for less lights and try to use bays where the lights can fit between the rafters but that's hard to do and in most cases customers don't mind having lights to be offset to keep the ceiling grid as high as possible, unless you have a high basement and you have room to drop the grid and still have a high ceiling then it's not a problem.

Good luck