Headwind down the stretch at the track I play is very important. If the horses are spread out fairly well entering the stretch, they have a tendency to stay put and not make big moves. A general trend, But this is from one track.

The mud, slop, or other addition of large amounts of moisture is what baffles me the most because every race the hoof strike of the horse in a different part of the track changes. A horse might get a good compact hoof strike on one stride, and then hit a spot where they cant push off, and then hit a spot where they dont even seem to enter the surface, just kinda slide. Very difficult that H2O mixed with sand and dirt.