Thank you Thomas.Behr for your for your post. I appreciate your taking the time to help me. That solved the vertical break problem.
But the way this is working is strange. I had originally set scaling to 0.75. That greyed out the Poster Rows/Poster Columns fields. But there was a greyed out default "1" in each setting. That was being ignored and I was getting the vertical page break. I changed the scaling to "automatic" as you showed; that un-greyed the 'Poster" fields. I manually put "1" back into each field as you instructed. Then it worked as you described - no more page break.
But now the bottom half of the lowest node was being truncated. I changed the scaling back to "0.75". The Poster settings got greyed out again but this time the greyed out "1" settings were recognized. So I don't get the vertical page break and I don't get the bottom node truncation, which is good. But it seems that starting defaults (Poster "1") don't work until you manually re-enter them.