I agree with 'Say again s l o w l y'. Using power to adjust a glide approach rather defeats the object of the exercise. The reason for practicing a glide approach is training for the day when it becomes a reality. Then at least the picture is familiar when the brain falls out of the sitting regions after an engine failure. However, once the glide approach has been mastered then positioning for the glide approach can be altered using power. Why not simply adjust your position in the circuit pattern to accommodate the glide from 'low key'. We used to make known our intentions for a glide circuit before turning upwind so that others in the pattern can adjust their circuits as well. Undershooting/overshooting is adjusted by altering the finals AOB. That's why you should not pick a landing spot straight ahead. Full flap should only be used when landing is assured. Initial ballooning on selection of full flap has on one occasion that I know of, enabled the clearance of a hedge.