but, if you are playing like that (3-D), i don't understand why you wouldn't be able to flame across height bands... ???
As I said, it's strictly a theoretical issue. I'm perfectly happy with the abstraction that 3" height bands represent, BUT had I house-ruled the game to the point where I needed to worry about the exact 3D volume of a template, height bands as a discrete representation of a unit's elevation would exist no more. And if there were no height bands, there'd be no need for any restrictions other than those imposed by facing, special unit rules and common sense to where exactly you can aim a directly placed template.
Hmm, now that I think about it, allowing free 3D aim would make the Flame lance an interesting point-defence AA weapon. This calls for further experimentation - are there any Finns interested in a series of playtest evenings around?
It seems to me that the rules do state that you can't flame across height bands (from what people have posted)
Don't rely just on what people tell you; check the paragraph on directly placed templates.
and that if you are at the same height band you just assume that the flyer who is breathing fire (or whatever the template's origin is) is at the same height in inches as the other flyer before the flame occurs.
Or close enough (say within an inch or two), allowing for the inevitable altitude variations in muscle-powered flight, some degree of aiming, not-exactly-represented terrain and a multitude of other insignificant things that get abstracted away by the game mechanics in favour of a manageable gaming experience.
Plus most flyers are physically large models that take up most of a height band anyway, so slight elevation differences would matter even less.