I just got the perfect cast. I may have just got lucky, but I perfectly lined up the sliding bar. Sometimes I think there might be a slight delay after you hit the button. Tho I'm not sure.

It was on a close fish to the right of the dock. I'm not sure if putting the cursor right in the middle of the shadow matters or not, but it if does it made it easier that the shadow was bigger, and when you do the perfect cast the animation shows you cast it directly in the middle of the shadow.

But yeah, just letting you guys know that it's definitely possible