Form 2210 - always required with varying income?

If my income varied during the year and I paid estimated taxes, when doesn't Part II Box C apply? Box C says "Your income varied during the year and your penalty is reduced or eliminated" by the annualized method. Any independent consultant or investor has varying income, so do they automatically have to file Form 2210? Does it make a difference if I paid equal quarterly installments and satisfied the safe harbors?