And in level flight you get best L/D at minimum drag speed. This will be at about 4deg alpha on a conventional aerofoil. In a glide, lift required is less than for level flight, so you should reduce your speed from Vimd as you now need less speed to balance the reduced lift while holding 4deg alpha. It makes very little difference in glide angles down to 15deg, so you can keep Vimd and be happy. In steeper glides you should reduce speed by a factor proportional to W times Cos(glide angle)
Dick W