You may wish to start with the safe envelope parameters of your glider for turning in a landing pattern, in other words, speed and bank angle. A glider turning a half circle at 50 knots (V 1.2 stall) will be much closer to the runway on downwind than a glider turning at
150 knots (V 1.2 stall). From the diameter of your safe 1/2 circle glide (and altitude loss),
you determine your safe minimum distance from runway on downwind. Of course, you can come in a little higher (and a little farther away) and "square it off" into a downwind, 1/4 turn, base leg, 1/4 turn, and final.
But the safe turn is the key. Too slow or too tight could lead to a bad situation near the ground. Not a good time to stall. Hopefully your airport is "glider friendly" and a suitable landing pattern can be worked out.