@tony -

Banning after a single attempt could actually get you into trouble. I personally ban after more then 5 from the same IP address IF it is a foreign IP.

The particular reason for this is the potential for legitimate traffic. If a user spoofs the IP Address from let's say your hosting server (or they attack from your own hosted network), then you could risk banning actual customers.

So even if %100 of hits going to /admin files are hackers that does not mean a hacker is not on the same IP address as real visitors.

You might be better off to limit access to anything you can to your own specific IP addresses and "deny all" from wp-login and admin sections, then allow what you need.

you can control your own access if you are the only one and give yourself a little leeway for hosts that change your IP address by dropping the last octet when you ad your IP range into htaccess.