As above - they'll know if and when to go into the shade.
MIne graze for a while in the full sun, then lie down to cud in the shade next to the shed (shed is closed as they would break the milking machine if left to go in by themselves...
), they all line up right next to the shed to be well and truly in the shade!.
Re fly repellent - are they actually bothered by the flies and/or midges? I only ever had one goat (not bred by me) that was bothered by them, and would shout to be let inside when they got too bad. So again, if they are not restless, shaking their heads swishing their tails or do whatever else they do if they are annoyed I wouldn't worry. For my girl it was enough to let her into the shed.