EMI shielding Tips for High Mag Field Compass Error

Hello,

My quad design is very compact, such that the Here GPS is placed 2-3cms above the li ion battery and so is Pixhawk. Hence there is high mag field error that appears.
I tried compass mot calibration, it did help, but when I use a different Li-Ion pack the error re appears. I have tried covering the GPS with copper tape underneath but it did not make much difference. All power cables and servo cables are twisted and as short as possible. Are there any other suggestions that could help reduce the mag field interference?

Thanks

Mumetal is better than copper.

But the best solution is a GPS mast