On their website's care tips page (
http://www.hartsteel.com/honing.html), they state:
"At Hart Steel, we use one layer of electrical tape, to protect the spine, while honing. The tape is placed lengthwise on the spine and then folded over the sides. The tape is optional, but we like it."
I don't have a Hart Steel razor, but am really tempted to get one. Since as Glen says their spine is that narrow in relation to the width of the blade, using tape to increase the angle sounds like a really good idea.
Thanks,
Jeff