Try tightening the bolts like this.
1 3
4 2
I'm not postive it'll work, but I ride BMX freestyle or whatever you want to call it and we have to tighten our stems (things that hold the handlebars) that way because it provides even tension and keeps our handlebars from slipping and moving.
The numbers are in steps that you should tighten them. The concept is to even everything up by tightening the opposite side of the screw. For example, you tighten 1 first, then you tighten 2 and it evens the tension with 1. Then you tighten 3 and it unbalances everything again, but when you tight up the 4th one, everything is straight again.And just make sure you apply the same ammount or torque and rotations to each bolt.
I'm sorry if you already tried this or already knew about the concept. I just explained it all because not all people know about bolt tensions haha.