flotu is right. The reason beginners are pointed in the direction of FR when they first start is because it is that little bit easier to develop a basic winning strategy that doesnt rely quite as much on adapting to individual players.
In other words, its probably slightly easier to become a winning player at full ring.

If youre already comfortable at 6max then there isnt any reason to change.
Youll probably find yourself playing a fair bit of both in time anyway.