Airgun Technologies VIXEN Where is the restrictor on the sub 12 ft pound version

So apparent the specialist gun tuners improve the shot count and FPS variation by removing the restrictor in the sub 12 ft pound models and simply adjust and balance the Regulator and hammer spring tension for more efficient air use and consistancy of around 11.5 ft pound. But I cannot find where this restrictor is located on the Vixen. Any of you guys now please?