It is easy to make the base leg too close because:-
The field is probably small compared with your home
airfield and relatively speaking your base leg looks correct
although it is actually too close (similarly High Key, above)
At Dunstable our base legs are usually rather close anyway
because of topographical features
At Dunstable we tend to learn circuits off the winch – which
are usually therefore too low and close-in !!!
Use FULL a/b to correct height if required, then close/lock
Can you sideslip your glider safely?
No low turns !!!!!!!