You shouldn't need an AOA gauge to understand that at a slow speed reducing speed increases your AOA, which will decrease your gliding distance.
Decreasing speed from 1.3 Vso to close to stick shaker speed will not stretch the glide at altitude. It does in the end game, and allows some airspeed to 'flare' as opposed to hitting the ground at whatever sink rate you have at, or close to, stickshaker.
Reducing flaps from 25/30(Landing slat configuration - full) to 20 (Takeoff slat configuration - mid) might be critical to improving your gliding distance.
Obviously the lowest drag configuration is best, but sometimes the gain achieved via decreased drag doesn't make up for the increased sink rate generated by the need to increase flying speed to your new, and faster, approach speed. Early? Yes. Late? No. Beats me what the actual difference between 'early' vs. 'late' is. That's the gut check time.