PowerDot applies electrical impulses to contract or twitch your muscles. The electrical impulse always flows between two points, with one point (or channel) beginning at the rectangular pad and one round pad and the second point/channel between the rectangular pad and the second round pad.

Therefore, if you disconnect the round pads, you won't be able to feel any muscle stimulation at all.

The following factors could be attributed to the difference in your feelings:

• Positioning of the pads - If the rectangular pad is located closer to the nerve or muscle motor point, the brain could be prioritizing the stimulation feedback signal between the pads. Feel free to experiment with pad position of round pads on the muscle in order to see if you can find a position closer to the muscle belly (where motor points are usually located).   
• Muscle fatigue - If the muscle fibers under your round pads are significantly tired compared to the muscles under rectangular pad, a higher intensity will be required in order to notice the difference.

In general, if you can see a contraction or twitches under any of the pads, there is absolutely no reason to worry, as your muscles always contract along its full length, between the rectangular pad and each of the round pads.