TCP vs MPTCP performance

I have been doing some TCP and MPTCP (modified kernel installed) measurements betwen my Linode and a machine in Norway.

With TCP (single TCP connection, traffic from Japan to Norway) I barely see losses. Actually, mostly, I see the transfer of 128MB to finish within a couple of seconds (10-15s).

When I repeat the same measurement with MPTCP (2 TCP connections in parallel) I see considerably lower throughput.

This is all fine. But since I am doing these measurements for research purposes to evaluate these protocols, would be possible to know if you have any optimization for TCP and if I am using MPTCP, which is an extension of TCP, but with slight differences in the packet headers, this does not happen?

I can send you one of my plots, if you are interested.