I assume what you want is to have the same apparent margins on the landscape pages as on the portrait. For example, let's say that for the portrait pages you have 1" margins all around except a 1.25" Inside margin (left for recto/odd pages, right for verso/even
pages).
This means that the landscape pages will have 1" top and bottom margins, with 1.25" alternating from left to right (the "inside" margin). But what you want is 1" left and right (which will be the bottom and top when bound) and 1.25" top or bottom (the Inside
margin when bound). This can be accomplished, but you have to enable Different Odd and Even if you have not already done so. This gives you separate headers and footers for the odd and even pages. This is a document setting (you can't set
it for just selected sections as you can Different First Page), so if you hadn't already enabled it, you will find that you have to copy the content from the
Odd Page Header (the Primary header) into the Even Page Header.
Unlink the landscape sections from the preceding and following portrait sections. In the landscape sections, set the left and right margins to 1" (they'll still be "mirrored," but they're the same). Then in the Odd Page Header, add enough Spacing After to
the header text to push the top margin down to 1.25". In the Even Page Footer, add enough Spacing Before to push the bottom margin up to 1.25".