In shoulder in, the inside leg should be ON the girth (or where the girth would be, if you are riding without one, lol!). So from a normal leg position, inside leg moves an inch or two forward for SI. Outside leg will naturally shift back a little. Shoulders turn in towards the centre of the school, eyes stay looking down the track. Eyes do not look down at horse's mane, mane is not about to change colour at short notice therefore there is no need to watch it....
I didn't realise just how far forward the inside leg needs to be until Francois got cross with me one day for doing it wrong, made me stand in the middle of the school whilst he told a tale about how James Fillis used to shred girths with his spur, because the spur was acting dead on the girth. Apparently there is a reflex point directly under the girth which when pressure is applied to it, causes a bend in the horse's body. So this is how you get inside bend in SI. Moving the inside leg back is just a leg yield really, regardless of whether the horse's body appears correct. I have ridden horses who appear to do a nice SI, but they only do it from leg yield aids, not correct SI aids! Very confusing. If ever I can't get SI on a horse who can supposedly do it, I ask the rider what their normal aids are, and they invariably move the inside leg back.
