fix mistaken dims & pos of me11 gas vols

Last attempt to correct ME11 ActiveGasVol dimensions (where simhits are produced) failed because the centres of ME11A and ME11B had been originally positioned too close together and I caused the volumes to overlap. This resets those positions correctly, and updates the lengths of each volume. This time I checked for overlaps using the Fireworks overlap tool (Thanks, Yana) and this time there are no overlaps dues to my changes.