Air Venturi Avenger bullpup bottle conversion problem

I recently purchased the doux bottle conversion kit and the hadjimoto bullpup adapter. When I tried to put it together, it wasn't long enough to screw the short tube in without pushing the picatinny/triple barrel band back. This prevents the gun from cocking or fitting back in the stock. Anyone here install this setup on their avenger bullpup successfully or have a fix? Any help appreciated.

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