"Against Liverpool at home we play perhaps our best 45 minutes against a top four side this season. We do that while missing a host of regular players but our level was nevertheless so good that day. And we end up losing 4-1. It happens," the Brentford manager explains, conceding they "simply have the ability to go to a different level".
While tough to play against, there are also differences in their style play which managers like Frank tries to exploit.
"Arsenal and Manchester City are very alike with two managers having worked a lot with each other. They've clearly borrowed some ideas from each other and it's sort of the Master and his apprentice but they are both incredibly good managers.
"What they try to do in their game plan is fairly similar with the differences lying in the type of players they are fielding. Liverpool are different to the other two, as defensively they are a bit more open to play against. They have a higher back line which presents more opportunities on the break against them, compared to Manchester City and Arsenal.
"On the other hand, Liverpool are also more difficult to handle in their offense, compared to the other two. It is certainly not easy to shut down City or Arsenal, but it is harder to shut down Liverpool," Frank believes.
During their three years in the Premier League, Brentford have at some point managed to beat all the so-called Big 6 and Frank admits to taking great pride in achievements like that.
"Of course, I do. If you don't, you're simply not humble enough in my opinion. We have a fantastic group of people and players here and I am very proud of what I am part of here at Brentford," he adds.