Contains the size of the bet that edges the current trade.
It is used normally with bet of bid type * that means if the size is positive create a bet of type back, if the size is negative create a bet of type lay.


<bet index="3" bid_type="*">
<place condition="dbo.fn_betproperty(@id_trade,2,'status') = 4"
    price="@edge_price" size="@edge_size" />
When the second bet of the trade is fully matched, creates a third bet to edge the profit&loss of the current trade.