Hi Barrier as a filter has many variables. First being the course. Second being the distance. Third being field size. Fourth being surface condition. fifth being rail position. another factor is prevailing wind. A good jockey should overcome all these. Unfortunately some get boxed in. You will find that on some courses >barrier5 will be a winning factor whereas on another course it will make little difference. If you split the number of races to each of these variables then the sample will be too small to be objective. I remember reading that UK racing has a program that will give the value of a barrier for a distance and field size for the major courses. Some barrier draws are utter losers.
Regards Beton