The ideal amount of knee bend is the same between these two kicks and it’s about 120-degrees of knee bend. You don’t need anymore knee bend than that
Just like Freestyle, Backstroke is a long-axis stroke. This means a swimmer rotates around their longitudinal axis. Keeping that in mind, and the fact a swimmer’s BEST body position is with the body about 2/3 under the surface of the water and 1/3 above—making sure your Backstroke kick is efficient is imperative for your races.
It is the down-kick portion that is the setup in Backstroke, while the up-kick portion is the propulsive phase. This is the opposite of the Freestyle Kick, but the reality is the same—you NEED a great down-kick, in order to follow-through with an amazing up-kick. Remember the bow and arrow analogy? If not, let’s review it.