Just my 2penneth folks as "an artiste" (LOL
).
The Parc Ferme area at Cadwell, as gorgeous as it is, is a bit pants in terms of it's photographic beauty.
If you can wangle it, how about have the riders in rows (say 5 peeps wide or whatever's needed to fit them all in) sat on the track surface going up the mountain. That way you get natural height increases as each row goes back, thus all faces are seen. Said photographer can stand on the grass between the track and the public fencing, that way, he/she's elevated above the track surface by about 3 foot too. Main considerations are where the sun (if there's any) is present and if you can get access to the track for the shot.
The mountain is a focal point on Cadwell and is a bit of a novelty feature for such a photo that would make it different to all the "riders sat in chairs in rows" type group shots you get (and that I've taken myself at BSB).
Have fun... Guy