BruteForce Blocking/Filtering

Hello Fortinet Community. I hope you have ideas on how we can solve our problem. At the moment we have massive problems with BruteFrce attacks on our Fortigate 100F - V 7.2.9 - Our users connect to our company network via FortiClient VPN. The bruteforce attack uses frequently used names in our country, such as Smith, Meyer etc. and exactly these users are blocked daily. Now the question is whether a Mac address filter or the OS check can be used here or whether the whole thing is useless, as the credentials may be queried in AD beforehand and only then is the OS, Mac address etc. checked. We were unable to find this out from the documentation. Thanks in advance, Alex.