James-Sorry, but I am not aware of any free source for the standard. Although by searching the Web, you can piece together more than enough EN 13537 standard information to use as a highly informed consumer.
On your second point, remember the torso blanket is used in addition to an existing quilt. The body is already completely insulated by the quilt and sleeping pad. The torso blanket is, primarily, further reducing natural convective heat loss. The torso blanket's item clo is not higher because it is a small area. It is high because it provides 3" of uncompressed 800 fill goose down. If the torso blanket covered the whole body, it would be approximately twice as warm.
800+ fill goose down is not only light for backpacking, it is also warmer for a given thickness. This is because it has less solid material to conduct heat and finer fibers to reflect more radiation. Solid materials, feathers and down quills, have a higher conductivity than still air.
The theoretical limit to the insulation provided by still air, at 32F, is about 6.8 clo / inch and the highest quality goose down (800+) = 6.6 clo / inch. By contrast, standard down (550) = 4.5 clo / inch, and Polarguard Delta = 3.1 clo / inch.