BN2 + Gliding cannot be used in the same sentence!
It's always hard to tell unless you've glided it with both props feather. It's suprising how far an ATR, DASH or SAAB glides with the props feathered vs dropping straight down with them windmilling. The ATR in particular tested this theory over the Med and the crew didn't really step up to it, report finding they could have easily avoided ditching had they maintained the correct speed and feathered both engines timely.