@EarnestAl’s explanation is the right one. However I want to point out a better choice for your position reference.
To have your shapes repeated, the anchor must be associated to the header, i.e. To paragraph on the (possibilby empty) header.
But, according to your description, the position of the shapes is not at all related to the header. Then choose as the reference (origin):
- either kbd>Page text area, where this area is inside the margins limit,
- or Entire page, where the whole page, including margins is available.
The benefit of choosing such references is to be independent from the effective contents of the header which may change with text volume, font size, spacing, …
PS: when asking here always mention OS name and LO version (because of subtle differences) and save format (only .odt allows to keep all suggested formatting).