Let's talk about the three instances of the "Flying Dragon":
1- The slash that beat Ryuuma was a melee slash but Zoro needed to fall from a high position towards his target to perform it. Very explicitly close-range.
2- The slash that cut the horn wasn't intended as a long range slash, as it was the same technique he used on Ryuma. Zoro just messed up big time. Here's how.
He started the fight using too little haki to prevent losing control of Enma, which is why an onigiri straight to the neck + a combo slash from Killer didn't do anything to Kaido.
Then he tried to up his output of haki (by his own words) and he accidentally went too far. Which is why he sent an absurd long-range slash that had him panting from the amount of haki he had wasted. It's not too different to the first time he tried to use Enma: he tried to cut a tree right in front of him and accidentally cut up a giant cliff.
Since we have seen him use the move on Ryuma, we know the intended use was a more controlled fire-based close-range slash.
3- The slash on King was just a powered up KoH Santouryu version of the slash that sent him propelled towards the opponent. Very explicitly (for anyone except Rootbeer) close-ranged).
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Now let's talk about the name "Flying Dragon".
Many of Zoro's attacks have
always had animal/beast patterns. Onigiri (Oni), Toragari (Tiger), Toro Nagashi (Wolf), Tatsumaki (Asian Dragon), Ushibari (Bull), Gazami Dori (Crab), Karasuma Gari (Crow), Ichi Gorilla (Duh), Hyokindama (Leopard)... I remember on Water 7 he also imitated a Rhino for one technique.
Then we get "Flying Dragon",
Hiryū. This is the kanji used on the name of the technique: 飛竜 . What do you get if you put that kanji in Google Images? European Dragons. Because "Flying Dragon" is a word-by-word translation, but that doesn't make it a good translation. Hiryu is how the japanese refer to drakes, to classical european dragons. There's nothing else to the meaning of "Flying" in that name.
Want another proof?
This is the silhouette of the attack, a
Hiryū, a normal occidental dragon. All Zoro does is imitate the creature for a fire-based attack... that as we have seen, is an airbone close-range attack.
That'll be all.