There are just so many variables - every situation is different in regards to what each of us uses - the wax or wax/blend, wicking, jar size and shape, environmental issue, etc etc etc - that is why what works for me might not work for you
That being said, I was told by someone many years ago that if any FO was not strong enough for me at 6% then just forget it and move on to one of the other FOs that are out there - and there are a million others that are out there! - plus there is the economics of it - that $15 bottle used at 6% is a $30 bottle at 12% - I think you find some knock-your-socks-off higher end FOs might actually be cheaper because you use less