Well it may be far off but if the cell is set as concentric in some vendors (Not Alcatel) the MS measures the BCCH of the serving cell to take decisions of Handover based on coverage of GSM (in Alcatel and some vendors there is an offset_HO_Margin_Inner to cater for the difference). It might be that case and in that case the level for serving being power controled should be lower than that reported in the neighbour window.