Boy, this is getting complicated.
Ully, let's for instance say that there were 2 buyers, you for 1 monitor and someone else for 37 monitors. Would you then still want to bear 50% of the shipping costs? I don't think so.

You would probably say something like: "Hé man, you don't mind taking one extra monitor with you, do you? I mean, it's no difference for you because you have to ship the 37 monitors anyway."

No offence meant of course.
I did some math. If we would do it the way that I suggested, you, with your 3 monitors, would pay 5% shipping (to Rav's place) per monitor extra as to opposite your way. This will be
less than € 0,50 per monitor extra (based on a certain estimated shipping costs). However, in your way, the guys who bought for instance only one monitor will have 216% extra shipping costs,
which means € 17 extra per monitor (based on the same shipping costs)I certainly know what is more fair.

I rest my case.