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Physical therapist here. OP, I can't address the pain in your calf since I can't see and touch you but I think this is the likely reason for the difference in your ankle motion: when you are standing and bending over, your calf muscles are stretched, esp. the gastrocnemius muscle. This muscle crosses both the knee and the ankle joints. When you are sitting, most likely you have your knee slightly bent and that puts the gastroc in a slack position => you can bend ("dorsiflex") your ankle more.