Going back to the original question.
(1) Always be aware of the details from a suitable guide of any airfield that you'll be overflying. It's important that you know what may be going on down there before you get close.
(2) There are several options,
(i) if overhead joins are not permitted fly directly over the airfield at above circuit height,
(ii)if overhead joins are permitted, at-least 1100ft above circuit height;
(iii) fly such that you will be aligned with circuit traffic.
(iv) fly sufficiently high (well above the ATZ or MATZ) that no conflict is likely.
(3) If an airfield has radio (whether it has an ATZ or not), you should talk to it. If entering an ATZ, you obviously need permission. If you are already on another frequency and don't have a second box, then a series of (slightly non-standard, but entirely clear) calls along the following lines would do the job
"Yeovilton Radar, G-CD"
"G-CD Yeovilton, pass your message"
"G-CD will be flying overhead Compton abbas, changing frequency temporarily to Compton Radio"
"Compton Radio, G-ABCD"
"G-ABCD, Compton Radio, pass your message".
"G-ABCD, Courtesy call no service required, will be passing through your overhead at 2100 ft above airfield height at minute 52, have you any traffic to affect".
"G-CD, thanks for the call, normal circuit traffic, we are on runway ** left hand circuit".
"G-CD"
"Yeovilton Radar, G-CD back with you".
"G-CD".
G