gitzo 2541 and RRS BH-40 ballhead question (main lock knob woobly)

Ok I just got my first tripod and ballhead I screw BH-40 onto 2541 plate but even screwing it tight it still sometimes got loose. Are there any tricks to tighten it properly or I'm doing something wrong? Also is the main lock knob on bh-40 supposed to be a bit wobbly? I mean I notice you can pull it (there is spring or something) and then you can change it;s position in y axis for better orientation when tightened. BUt even when tightened you can feel a that it's a bit loose. Is it normal?

I believe there is a set screw on the 2541 base plate that you can use to prevent the ballhead from loosening. Also, if you cannot hand tighten the ballhead use a strap wrench to give you a little more torque.