The True Range of Fire Demon

 Range of Explosion

 Range of Fire Demon

Looking at where your standing in your picture, it would not be difficult to superimpose my pink boxes on your picture. It's quite simple to see that you are out of range for your first shot on the Leprechaun with Fire Demon. Since the circle coming off of Fire Demon is quite large and is drawn over your character, it's easy to assume that Fire Demon's range is smaller than it really is.

Maplestory defines pixels as the distance by creating two points - one to the left and above you, and one to the bottom and to the right of you - to create a box. The reason why Teleport is different up and downwards is because it is not dependent on a box, but rather a simple "distance" value marked in the WZ files. This distance value is then reinterpreted based upon which way you are teleporting. Gravity is not an issue when calculating the two (x, y) coordinates defined in the WZ files.

Explosion has a box that is sized 400 x 300 (200 to the left and right, 150 top and bottom - your character in the center). Since Maplestory likes to use the X range to one side of your character, this is why it says "200% range" for Explosion. However, since the X range for Fire Demon for one side of the character is 300% range, thus it's defined so in the Fourth Job Skill Tables.

If you just want to go by which skill has a larger AoE, then Explosion wins hands down.

Explosion's AoE = 400 pixels * 300 pixels = 120,000 pixels
Fire Demon's AoE = 300 pixels * 100 pixels = 30,000 pixels

If you'd like to see the WZ files for reference, I can supply them.