Teaching on the Bulldog was that the upwind turn should be flown at 15~20° AoB at 80KIAS, starting at 500' in an 800' height circuit.
But that was only because we flew 'racetrack' circuits rather then 'square' circuits, so the specified parameters achieved the normal downwind leg following the continuous turn.
'Inter' flap was selected downwind, with the speed decaying to 75KIAS. At the '45°' point at the end of the downwind leg, again a continuous 15~20° AoB turn was flown to final, rolling out at a height of 400'. Then it was full flap, 70KIAS and point/power to touchdown.
Hence although I can see the relevance of 15~20° AoB when flying a 'racetrack' circuit, it is nonsense for the usual civilian aerodrome 'square' circuit - where the only 15~20° AoB turn might be the initial turn to the crosswind leg, in order not to reduce the climb rate. But all other turns should be made with around 30° AoB, to limit the amount of time needed in the turn when, in high wing aeroplanes, your view of others in the circuit is reduced.
In HM's Gnats, around 60° AoB and pulling to the buffet nibble was often the way we turned from take-off to downwind - don't try this in a spamcan though!