how is the middle of a folded Brompton supported? I have a Brompton customised by Kinetics and notice that when placed on its side the upper parts seems to be supported by:

at one end, by the frame hinge, and
in the middle (near the fork catch) by the front hydraulic disc brake caliper body pressing against the chainring guard.

There appears to be no other support, so if something is subsequently stacked on top of the bike, I'd guess it would stress the caliper and crank/chainring. Shopping-trolley mode with a loaded bag may also cause pressure between these parts.

How does a normal Brompton, lain on its side, support itself in the middle?
How much weight can sensibly be put on top?

The reason I ask is that I bought a chubby trailer which can hold the brompton but it provides no protection against something heavy being placed on top of the bag in transit. Given this problem with the custom Brompton I am curious as to how a normal Brompton behaves.
In case it make things clearer, I'm thinking of the brompton on its side being like a &lt;, where the point is the frame hinge, the top is the handlebar side and the bottom is the rear triangle side. I'm trying to find out what contact point (or points) along the inside prevent a normal brompton flattening into -.
I don't have access to a normal brompton and have been unable to find detailed images of the inside of the fold. I'm fairly certain the middle isn't supported by the fork hook (that stops the fork moving outward, not inward). I'd guess the left fork blade eventually comes into contact with the right chainstay and that contact point provides the support but it would be nice to know for sure.

Here are a couple of pictures of my (not-very-clean) bike.
Despite appearances, the only places that the left side (front-of-hinge: fork,handlebars,etc) and right side (back-of-hinge: frame, rear triangle, etc) will be in contact when the bike is laid on its side are at frame-hinge and brake/crank (circled in red):

Close-up of the brake/crank contact point:
From a phyics or engineering point of view, I don't know, something on the order of 20/30 kgs, maybe?
From the warranty and manufacturer recommendation, the answer is 0.
A folded Brompton (and other foldable bicycles) are not supposed nor meant to carry any weight.
You can still revert the order on your trailer, put the heavy stuff on the bottom (which is  in any case a meaningful thing to do) and then the Brompton on top, fixed with some bungee rope or with some other kind of band/belt.