set a full page figure in master document

I have a master document with several sub documents. in one of them I set a full page image which I want to be in a fixed page inside the subdocument. for that i insert the image and its caption inside a frame, and I set the frame anchor to page, and wrap to none, so the text flows around the frame leaving it fixed to the page. When I insert the subdocument in the master, the frame disapears!. it reappears when I set the anchor ‘as text’, but text flow gets messy, as I obviously get a lot of white space.
What would be the correct way to set the image page-anchored in the master document ?
thanks in advance, hope the situation is well explained.

ok i think i have found a tricky wrkaround. if I set the anchor to character, then the frame will occupy the full page that follows after the page where the anchor character belongs, and seems to be that this relative position is conserved in the master document and pdf export. however, if I set the height of the frame to 100% of paragraph area, the wrap is automatically set to ‘through’ and a lot of text gets lost behind the frame. in order to solve that part, the frame height should be 98% of paragaph area, so the wrap can be set to ‘none’ . quite wird but seems to work this way. can it be done in a cleaner way ? thanks in advance.