OpenVPN slow over UDP, fast over TCP

[jstip]

Hi, I've been looking for quite a while now to solve this, but I can't find what to do.
My OpenVPN connection is pretty slow over UDP (around 100MBps), while over TCP, I can easily achieve 400MBps+.

I tried changing the tun-mtg and mssfix settings, also based upon a run of mtu-test.
I tried changing sndbuf and rcvbuf from 0 to 393216 to 524288, but I can't get near the speeds of the TCP connection.

Can anyone advise on how to fix the performance for UDP? What can I check or update?
For now I leave the connection to TCP, as this works better now, but this is not optimal of course.

Thanks.