If we have a network topology (in Mininet / Linux) like this:

Every link has a speed of 10Mbps.

If I do measurements (connect at the maximum capacity) host1 with host4, and at the same time I connect host3 with host2 => They do not interfere with one another, I see on both sides a speed of 10Mbps.

BUT, when I do measurements (connect) host1 with host3, at the same time I connect host2 with host4 => Both transfer rates go down (6Mbps), so they are interfering with one another. Why this is happening when the distance and speed are the same at all scenarios? Why in the second scenario we have interference?

host1 host3 switch1 -switch2 host2 host4 host1 host3 switch1 -switch2 host2 host4