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The Y-position (distance from the top of the document reference): -6px, similar reason as X-position.
Width: We can now use formulas (by clicking on the formula button) and write page.width+12px (we need to add 12 px, to compensate for the 2 x 6p bleed)
Height: Page.heigt+12 px, same as the document + the compensation for the bleed
From now on, the image frame will keep the same size as the document.