If it feels like your UPRIGHT GO only vibrates when you are very bent over or moving slightly rather than when your upper back is slouched, please try the following:
Place the device higher on your upper back and calibrate it again using the app or by double-clicking the power button on the device.
Change your device’s delay by tapping Delay on the main screen, and/or adjust your Upright range by going to Settings > Advanced > Upright range.