Does the 100 yard line have target holes like the 25 yard line?
Considering a detachable top for my frame too. At 25 yds standing I'm seeing all grass in my backdrop (I am one of those basketball tall people), and at 50 I've only got about a foot or so of berm and I hate to incur range god wrath by hitting grass.
Yes, the drawing has an error. the assembly drawing on the left has it backwards and you have to flip it around if you build it like shown on the right side. Otherwise, you just put the small yellow blocks on the other side. Consider it a test, if you can't figure that out when you put it together, you should not shoot.... you passed the test.
I made a couple wood wedges (like door stops) to hold the target frame tight in the sometimes shallow 100yd tubes. This works well