From Bet Angel forum:
Not entirely sure this is even possible, but can Guardian place a trade at either the highest or lowest traded range, perhaps using volume traded previously at a set price?
Bfexplorer Solution:
Bot trigger has access to any betfair api data. In my bot trigger code, the bot checks what prices had been already traded on the selection, and filters them by minimalTradedVolume (by default set to 5.0).
When at least two prices had been traded, the function getTradedRange returns minimalPriceTraded and maximalPriceTraded (code lines from 34 to 47).
In the lines 75 – 82, you can see how create list of bets to be placed by Bot Trigger in the line 82.
The bot trigger uses two parameters: MinimalTradedVolume and Stake.