I'm trying to estimate how much the idle thrust is contributing to the glide performance and how much the glide path angle will increase with two dead engines
In a simulator operation we assume the aircraft has arrived (5 miles from airfield) early downwind at 9000 ft after gliding (both start levers cut-off for the exercise) at 210 knots. Then execute normal flap extension to Flap 5 and glide at 170 knots. Turn base at 3-4000 ft. Flap 10 next. When certain of reaching field, gear down manually or hydraulically, and now ensure you are 10-15 knots faster than min maneouvre for flap setting to allow for flare. Dive the aircraft if required to land a respectable distance in and plant it firmly. The rationale behind selecting Flap 5 and 170 knots once you are in the circuit, is to reduce radius of turn required for 210 knots clean and makes judgement of base and final turn easier. .
There are certainly several other flap/speed/ combinations but to simplify for judgement and training practice it was decided to settle for one procedure. Caution: This is purely a personal opinion.