Ah right! The sentry doesn't aim towards the cursor, but rather mimics the angle Ant herself is aiming towards the cursor: this was done to allow full 360° control of the sentry's aim regardless of its position on or off screen, as well as to make it easier to use with controller aiming.
Hope this helps! If it still doesn't feel quite right don't hesitate to tell me, and I could work on an optional alternate control scheme.