For trolley pole operation, the wire should be more above the track center line on straight lines, when higher speeds are possible, in order to prevent sudden lurches of the (rather heavy) shoe.

On the other hand, there must be a zig-zag for pantograph/bow operation, in order to keep the wear on the contact strip even. The zig-zag has some other advantages, as it does inherently deal with thermal expansion (if it is not mounted rigidly to an insulator, but uses a short stretch of carrying wire or some other flexible support. Of course, nowadays, as soon as the power requirements and the speed increase, conventional catenary is used, with tensioning of the wire(s).

In curves, the tolerance for pantograph operation is the width of the contact strips (or the zig-zag on straight lines). That may actually mean fewer support points than needed for trolley pole operation, because of the lateral forces.

It is in some ways a bit of a surprise to see modern vehicles with trolley poles.

The position of the pantograph is either above the center of a truck, or with long wheelbase vehicles, above an axle.