OpenVPN Client: Download lower than Upload

I am running Openwrt on a WR902AC. I installed OpenVPN on that router and connected successfully to my home Network. I ran a speedtest and wondered about the Result:

Download: 6 Mbps
Upload: 10 Mbps

Why this difference?

When I disable OpenVPN on the Router and run OpenVPN Client on my Laptop i get 10 Mbps in Download and Upload. This should be the Maximum rate, cause this is my Home networks Upload Speed.