Dialogue is usually along lines:
Pass your message.
Glider XXX is 4 miles North West of your field at 4000’ routing overhead towards the wind farm. Request Basic Service.
Glider XXX, QNH is nnnn. Basic Service. Report descending below 2500’.
Nnnn, Basic Service. WILCO. Glider XXX
However on occasion I have been “cleared” overhead. Sometimes I'm instructed to report on reaching a certain point such as overhead or after completion of crossing of extended centre-line etc..