When I see movies or joke with students about doing the horse stance, get them doing it, like they are sitting on an imaginary stall and straining their thigh muscles trying to hold the position, then I say how this is actually an exercise of 'sitting in koshi' and koshi is like sitting on a super soft cloud or sofa. Only then will the thighs relax and the true feeling be experienced.
graham, how do i do the horse stance 'koshi' style. i cannot get the soft sofa feeling, my thighs can't take the position too long. can you go into more detail?