topsy, good post,

In my own form study I concentrate on class and beaten margins from last start, usually eliminating any runner beaten more than two lengths at it's previous run. Don't forget that it may have finished seventh, beaten 1.8 lengths in a 'blanket" finish........although the astute punter will recognise this as a very creditable run. This is the main flaw in mechanical selection methods which may stipulate: "must have finished no further back than fifth or sixth last start...", yet, the run indicated to the keen form student that it had "back me next start written all over it!"
I've taken note of your barrier position comments because recently I have fallen foul of backing horses in an outside barrier, believing that the skilful jockey on board could overcome this adversity, however, it is a big ask isn't it to be competitive after drawing the extreme outside and having to be "used up" to come over and take up a reasonable position.
Your comments on the SP also confirm that at "barrier rise" the prices being offered generally represent a true reflection of the particular runner's chances.

Cheers