I have an iOptron SkyTracker Pro. With my Canon 6D Mark Ii and a "nominal" lens (either 14mm or a 24-105mm), I have no problem adjusting the counterweight to achieve a good balance in any position.
However, I just purchased a Sigma 150-600mm lens that is rather long and hefty. When the lens pointed off at an odd angle (e.g., perpendicular to the polar axis, upward, and back), it doesn't seem possible to achieve a good balance in all rotated positions. I believe this is because the heavy lens moves the center of mass away from the counterweight axis. So in one position (say, 45 degrees), the camera side is heavier. But in another position (say, -45 degrees), the counterweight side is heavier.
Am I missing something or is this normal? I suspect that if it were possible to place a counterweight such that the center of mass was opposite the camera/lens center of mass, this wouldn't be a problem. But I don't think that's possible with the iOptron tracker.
Is the answer to just point the camera at the subject and then adjust the counterweight to achieve the best possible balance and hope for the best as the tracker moves during the shoot?