For reference, LDView's default zoom level is calculated based on a minimally sized sphere around the center of the model's bounding box. The default zoom level puts the edge of that sphere at either the top/bottom or the left/right edges of the window (or both if the window is square). This has the effect in LDView of making it so that no matter what model you load, if you rotate it without zooming, it will always be fully visible, while at the same time being as large as possible while satisfying this constraint.
LDView's Zoom to Fit, on the other hand, adjusts the view frustum (pyramid) until at least two of the edges touch the model, while the other two edges are equidistance from those edges of the model.
LDView's Zoom to Fit, on the other hand, adjusts the view frustum (pyramid) until at least two of the edges touch the model, while the other two edges are equidistance from those edges of the model.