Wes, I have noticed much the same and stopped betting in races >1600m ages ago.
Another thing I have noticed, albeit with no firm figures to back it up, is that 2.5, 3, and 4kg apprentices have a woeful record in races >1600m. This is because they lack pace and timing judgement IMHO.
Having said that if you can spot a good young kid early enough there is money to be made from them. A case in point is one certain young bloke in Brisbane, although everyone seems to be on to him now, worst luck.

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Jose'.