The rod is over lined when your usual ability to control the outcome of the cast is hampered, overridden by the line's affect on the rod.
Technically speaking, "The rod gets wonky"
Look for a forward loop that gets pulled open and will not come back into shape. As well, try to make a medium distance, medium speed, well mannered narrow loop and see if instead the loops tails.
Casting ability differs from one caster to the next. Ability, very importantly includes 'feel'. What one caster feels the other may not. This too has a technical description: The Goldilocks Effect. Pay attention to your Inner Goldilocks - the (your) truth often rests there.