Most popular solar tracking mounts that are not of the Azimuth/Altitude variety are what I call the "polar" type (aka dip-tilt).
I've been struggling with how to communicate this issue for quite a while and finally found a way to illustrate the problem using OpenSCAD to draw it in 3d.
In an astronomical style equatorial mount, the polar axis is fixed, and parallel to earth's rotational axis. The Declination axis of an equatorial mount changes the angle of the system relative to that primary rotational axis. Another way of stating this is that the result of the declination rotation is itself rotated about the polar (aka R.A.) axis.
The Dip/Tilt "polar" system maintains a northward direction but changes the angle of the primary/polar axis itself (the "dip" part). Because of this the effect of the rotation about primary axis is proportional to the sin of the "tilt" towards east or west. In other words, when we turn 90 degrees to either side it doesn't mater what the polar "dip" angle is: we end up oriented due east/west.
What this basically means is that the Dip/Tilt "polar" tracking system is only capable of covering a wedge shaped portion of the sky - which doesn't correspond to the season coverage of the sun. The fact that the dip-tilt system converges at a right angle to the standard polar coordinate system makes it poorly behaved from a mathematical standpoint.
The Mega Tracker b57 firmware release will fully support astronomical solar tracking with dip/tilt "polar" mounts. Solving the problem of converting standard polar coordinates into the dip/tilt coordinate system was quite the mathematical challenge. The Mega Tracker finds the minimum-deviation angle when solar position is out of bounds of the dip/tilt tracking coverage area for optimum performance. True and accurate astronomical solar tracking with polar, equatorial, and azimuth-altitude mounts is possible!