The typical easy formula to determine max heart rate is 220 minus your age. That of course only gives you a ballpark number. Is it correct to assume that for most fit people this formula doesn't work?

My max is 12-15 beats per minute higher than the formula says it should be. A good sign I hope?

I believe your max heart rate is determined by genetics not your fitness level. Intensive training may lower your resting heart rate and the amount of blood pumped with every beat but the max rate will stay the same. After training you will be able to output the same power at a lower heart rate.

220-age is pretty useless for the majority. The variation of heart size (and therefore max heart rate) is pretty wide. You may find 20 year-olds who have max heart rates of 180, or maxes of 220. Or even more.

Even if you figure out your max via testing, it's also a mostly useless measure. If you want to do a good job of setting heart rate zones you need to base that on a field test (or a lab test, if you want to spend the money). That can tell you where your LT is, and that's what you use to base your zones on.