Well listen to the fitter. Be willing to try their suggestion for at least a dozen or more rides. New positions sometimes require you to get used to them before you actually feel better.

However for calf and achilles tendon issues I'd have to ask if you have your foot too far back on the pedal and simply let it flex too much as you pedal. Moving the foot forward on the pedal may feel funny for several rides, but for me it has been an easy thing to get used to.