In my experience it is often true, CAS.
Easier to keep straight for one thing.
A horse running without anything around him is more likely to idle.
Horses on the rail tend to find more than those going equally as well / badly who don’t have a rail.
Noticeable more horses on the rail that are not going as well as their rival fighting back to win than those not going so well without the rail fighting back.
If I were betting in running in the final furlong it would certainly be something I’d allow for.
Value Is Everything