I had he pleasure of speaking to Ian Barnes on the phone a few years ago re info on a certain system seller, nice guy and a very helpful gent, (Ian Barnes that is).
I think that in his book Designing Sytems for the 21st Century he mentions 4th last start.

Just wondering if SP last start is a reliable indicator re the horses chance next start ie how much 'weigh' ,if any, would you give this factor when looking at the form?

Thanks Peter