Hi Dave
Was looking a the Ancient Red Dragon Kahn. It's space is 30x30 ft. If it uses its Fire Aura ability, it becomes a pillar of fire 10 ft. in radius. That means it actually becomes smaller than before and creatures that were adjacent to it before now won't be affected by the aura?
Also, could you please give a reminder as to why you're moving away from legendary actions. I personally find the extra reactions at a certain initative count and the usage of a potential opportunity attack to be a bit cumbersome, but most importantly, it deviates from the standard way of doing boss monsters, that everybody else is following. I'm afraid it could lessen the appeal of your work for (many?) people, which would be a shame indeed.
Do you have a link to a composite of these?