The problem with the last one is, if its long range, it wont fit.
If the graphic width keeps increasing it will be 2 wide, so I think that would be good for something else.
Idea #1
Make the Ion Cannon attack not an attack, but an ability.
2 Abilities:
1) Send a powerful burst of Ion Discharge (or something like that). 1 burst, about 100 mana.
2) Send a powerful beam of Ion Discharge (or something like that). Continuous
beam of energy shoots from Ion Cannon. Takes energy like cloak does, but 10 or so times faster.
Idea #2
Make the Ion cannon attack able to miss.
Don't make it an attack/spell that follows the enemy, it just detects where the enemy was and shoots there. If you use the Continuous idea of Ion Discharge then make it so you can control exactly where the beam is going using some advanced memory patching (make is so if u click on an area, the continuous attack slowly moves to target that location.) But remember, if it never misses, terran has a huge advantage. The game will be full of people building 10 Ion Cannons and eliminating all opposition.
Idea #3
Splash is Always nice
The idea of the first ability (1 burst) is displayed in the Battlecruiser attack in my beta mod,
Silvercraft, just in case you still don't understand.
P.S. I inverted it, the color is now Teal, not Blue. I had to make some minor changes, and here it is now.
[attachmentid=15372]
It looked boring without red electricity, so I added that in.