Can't get Open NAT when Xbox on static IP

I forwarded the correct ports on my router for my xbox to be Open NAT, which worked fine. However, I found the Xbox bouncing around on various IP's as I turned other devices on and off, which causes obvious problems since the Xbox can end up as an IP that did NOT have those ports forwarded.

I figured the easy solution was the force the Xbox to be a static IP (the highest # I could have, to avoid conflict), but when I do, the Xbox Live test gives the warning that the NAT is now Moderate instead of Open. Makes NO sense to me since I literally simply switched the Network Settings on the Xbox to Manual and typed in the info for the IP, Subnet, Gateway, and DNS (oddly the DNS primary was my router's 192.168.1.1, and the secondary DNS was 0.0.0.0). Why shouldn't it act JUST like when it's on Automatic and it shows those same settings (and doesn't warn me of Moderate NAT)?

Thanks