Leon indeed wouldn't travel thousands of miles to Crystal Mountain to trouble an adult Blue Dragon.
His rationality was indeed influenced to some extent by the Red Dragon body, but not to the point of madness.
However, now that the Blue Dragon had actually come over, hovering over his territory for some unknown purpose, Leon really couldn't find any excuse to be a coward; at the very least, he had to ask what the other party's intentions were.
To know oneself and one's enemy is to be invincible in a hundred battles. Leon certainly wouldn't charge in rashly; the first thing he did was to carefully observe the Blue Dragon, to assess it... The distance was too far, honestly, it was impossible to tell anything significant, unable to determine if the Blue Dragon was of regular size, or smaller or larger than average.
Under such a circumstance, he could only assume that it was a standard-sized Blue Dragon.