Patty nailed it perfectly...BRAVO. Basic subnetting is the rule here.
You can have a scope of any range within your assigned subnet, but you cannot cross subnet boundaries. For example: Network ID 192.168.1.0 SNM 255.255.255.0, range of addresses available is only 192.168.1.1-254. You cannot have an address above or below that range without changing SNM.
The range of IP's and the SNM you specified covers 8 network IDs: 160, 164, 168, 172, 176, 180, 184, and 188.
You would need a SNM of at least 255.255.255.224 to cover that range. Ask you ISP to verify the SNM again. They could be doing something weird, but I doubt it.
As for your network range in the scope, you do not have to use all the addresses in the scope. Using the same example as above, you can: 1.) choose 50-100 or 100-200 or whatever you need; 2.) put all the addresses in the scope and then exclude any that need to be excluded. And, you cannot have more than one scope from the same network ID, ie. 50-100 and then 110-150.
FYI...
Like Patty said...Why are you using public IP's when it is not necessary?
Hope this helps.
bob
I know what I know and that's all I know.