Beware not to make it too "rule-ish" or mechnical or systemmetised, these things don't "feel".

Ask,
Why did it come 4th then spelled, why was it spelled, why did it come 4th after the spell and was it an improver or does it have potential?

Consider further on-the-day analysis by watching prices, pre-posts etc.

At times nothing seems to happen.
To borrow that cliche, "nothing is a certainty".
If nothing is a certainty, I don't "get" an why E/W bet is 50/50.
More to the tune 75/25 - 60/40 the lesser on the Win accordingly.