And as you've mentioned, you're using a static IP for your Kindle over WiFi. That one has to be in your usual subnet to talk to your router.
But over USB, both ends defaults to a slightly more obscure private subnet because it doesn't (and shouldn't, to keep things sane) be in your subnet. You really only need to change the USB IPs if you are indeed risking mismatches.
But over WiFi, either you know the IP because you set it manually (advanced network setup on the Kindle), or it's assigned by your router via dhcp, and you get it either from your router (I'm assuming config UI and/or network topology maps available somewhere), or from the 711 (or 411?) page on the Kindle.
(I'm not mentioning the defaults to avoid confusion, because I, weirdly enough, don't use the defaults on my setup for portability purposes between legacy kindles, kindles and kobos
).
Take all that with a grain of salt, I've been bashing my head against mystical Kobo issues all day, so my sanity is a bit frayed ^^.
That's my systray right now. Yes, I was optimistic at the beginning, I went with kwrite instead of kate, and now I have seventy billion windows open instead of one, and it's a mess
.