The purpose of Go To Previous/Next Position command (in command list they are called Edit.NavigateBackward/Edit.NavigateForward) is to make navigation between visited position in document more easy. But it is not a direct history of your cursor movements.
Anchors are only stored in some commands as Go To, Find, Page Up/Down etc. So commands which can cause big jumps. Common movements of cursor to right/left are not stored. Mouse clicks are also stored as "anchors".
In addition to mentioned behavior, editor skips minor changes even for noted jumps, to reduce history size but have it in brief kind:
- if distance between last anchor in history to new less then two lines
- if delay between jumps is less then UndoMergeDelay (by default approximately 3 seconds).
Currently Navigation history is only work inside of one document, but it is planned to add document through navigation some when.