Yes I thought about the fff, nnn, etc. notation, didn't think it was that though, that may also just be read from the xml itself. Will have to do some testing with sub-windows to find out. For this test here I was just moving the map window around.
Regarding your editor, first off sorry for my useless bug report.
What happens is I edit one byte (editing in hex is perfectly fine, don't need dec) and save. Looks fine on the screen, but in fact your editor will change the adjacent byte as well to a specific value which seems to depend on the value you entered for the first byte. Happens reproducably all the time.
And maybe a word of explanation regarding how location in conjunction with what I call PackLocation works. Say you PackLocation is 2 for right, top. You HPos is 40 and you VPos is 10. The window will then appear at an absolute horizontal position of Screen Width - Window Width + HPos, and an absolute vertical position of 10. So your editor would have to take all those parameters into account. You could then offer options to automatically center a window, for example. If have yet to test it with windows that bring their own definition of PackLocation and PackLocationProp in the XML into play. Judging from modding experience with those I assume they will simply override all settings in the .ini file if any of them is present. For example, if I add a pack location of "cpc, cpc" to the xml and no PackLocationProp, but a Location that is off-center, when displayed the window will nevertheless be exactly centered. Will have to test this to confirm exact mechanics though.