Estimated Position In Queue (EPIQ) is imperfect since you lack detailed order information. But a conservative estimate can be determined by starting with the quantity at the order's price when it is entered. Then reduce it by any trades that occur at this price. Then adjust it further downward if the BidQty falls below this value.
The formula in the Branch0 block is as follows.
! tradeIsOTC AND tradePrice = MsgInfoExtractor0.limitPrice AND Order0 > 0