What is the attack roll of a telepathically controlled balista?

[Red Bear]

There is this very weird wizard archetype "Siege Mage" that grants the player the ability to telepathically control, aim and fire a siege engine. It doesn't describe very well how it works though. So if a player uses this ability (Siege Engine Bond) to fire a ballista, what is the attack roll? BAB + Dex? It feels weird to use Dex for a telepathically controlled object. Does he get a penalty for the size of the siege engine? Does he need line of sight to the target?

[Ninjaxenomorph]

Looks like it. Note, however, that indirect fire siege weapons use Int as the relevant attack stat.

[Red Bear]

Looks like it. Note, however, that indirect fire siege weapons use Int as the relevant attack stat.

I didn't notice that, thank you.