When trying to add my computer to static lease, I get the following error

I don't understand the reason for this. If I would want to assign IP from outside DHCP range, I would assign it statically locally on the device connecting. If I am assigning IP at the server, I see no reason I can't set it from inside DHCP range.
All previous routers were allowing me to assign within range.
Is it possible to turn off this "check" so that I will be able to set any address I want?