Page display - red box on thumbs keeps changing size and position Acro8pro

Hello,

New here and hoping someone can help me.

I am creating a children's book and have most of the issues worked out except that when I click a thumbnail only a portion of the page aligns on screen. I have resized the red bounding box numerous times but clicking back and forth between thumbnails changes both the size and location of the displayed area. Is there a way to set that red box and "lock" it into place. I'm using page height as the default view.

Thank you for any assistance.

Acrobat 8 Pro