It’s the blood of the person making the circle which empowers it.
that implies they're really just enclosing a space as part of themselves 🤔 and that all magic really does come from within 😂
Seriously tho, the real implications are with summoning. Implying to me to do so you're actually calling like to like with something inside yourself and just using the name as a vector, otherwise it looks more like GP's fishing. That.. that actually jives exactly with my theory on how Nemesis vectors in comparison to the PG summoning explanation...
See folks, everything adds up magically in the DF because I'm fairly sure Jim designed his magic system and then the world around it. The problem is is because of that order of operation a lot of what's going on is based on magic and the world around it specifically so he can't just explain it all. But as he's said he's left all the clues minus one important link in the logical chain. All we're really doing is solving for X. Where the other side equals how the world works/is ordered.
(I really hate encountering that line of reasoning on DF's magical system. It might have holes I haven't seen, but the structure hasn't outright broken that I've seen either)