As a moderator, I don't see advertisements, but there is one more space eater. The little panel to the left of the post holds your name and a brief note about your account's age and post count. The vertical page size cannot be less than the height of that panel. I have seen replies expand the page, although if you specifically used the "Reply" option that is at the bottom right of each post, if the post in question included extra blanks, I think the "quote" of that reply will also include the blanks. However, the Xenforo software "compresses" such replies and gives you a "click to expand" option inside a compressed quote. BUT if you use a drag-n-select highlight and then click the "Reply" option that pops up (i.e. selective reply) and the selected area includes extra lines, I don't recall that compression occurs for that case.
Then, there is the fact that if you have a non-trivial "signature" area, that isn't compressed on-screen either.
Needless to say, there ARE a few options to consider.
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