The other option besides having the feet tucked back behind (with the knee lower than the hip) is gonna be to have the feet out wide and usually out in front of the athlete. This is gonna be very common for bigger lifters, lifters maybe with a longer shin who aren't able to get that tucked back position, or if you just don't have the mobility in the quads and hips... we're still trying to achieve knee below the level of the hip.