Guidance for high pressure simulations

I am interested in investigating crystal polymorphism and I would like to know if you have some established best practices for high pressure simulations, particularly with anisotropic pressure scaling.

My current test system is urea and the first high pressure polymorph is Form III at 4800 bar with IV forming at 28000 bar. I tried running a simulation at 10000 bar with anisotropic scaling with tau-p=4 and compressibility=1e-5 and the crystal underwent an extreme fluctuation and settled into a presumably different polymorph.

This is probably a force field deficiency but I would like to make sure I’m not making mistakes with the simulation parameters.