Stopping distance

Sorry if I already posted this. I would like to know why trains stop at different distances from a red signal. I live very close to CSX’s Trenton Sub near Cp Nesh. there is a main and a parallel siding with signals at both ends. Some times the trains stop several yards from the signal ( behind the house) other times they stop much further down the track. Can any one tell me why?

Thank You Dennis ( vader225)

Five responses so far on your original question: http://cs.trains.com/trn/f/111/t/229770.aspx