If you are going to overfly an airfield please make contact first. Even if you intend staying well above the ATZ you may not know what's going on around you, like aerobatics. Where I fly from we have people leaping out of aeroplanes from overhead the field and well above the ATZ. A lot of people end up in a lot of danger if someone barges through unannounced. Ask first and you'll be told whether it's safe or not. If it's not, or you're just not sure (the field's non radio or no-one answers the radio) it's much safer to go round. After all, it's not that far out of your way, is it?