I'm current rejiggering large elements of my story, so I'm working with a 20-page treatment per my consultant's advice. The idea of keeping it at 20 pages is that it will help me go into enough detail to adequately explain the characters, plot and setting without giving too much detail until I'm finally ready to do a full rewrite. However, the problem I'm facing with my current treatment is uneven pacing. Certain expository elements can't really be reduced in size much, such as the backstory of a fictitious society that plays a big role in the unfolding plot; other elements, such as action scenes, can be reduced to one or two sentences. This poses two problems: One, since most of the exposition is towards the beginning, certain plot points such as the inciting event or turning points seem to show up nearer to the midpoint than to the beginning; and Two, I'm having a really difficult time gauging how long the story will be, since the amount of action builds as the story progresses. The current treatment effectively communicates everything except for the pacing. Is this a common problem for treatments to have, or do I need to go back and revise it?
I certainly feel like I have the same issue, but it doesn't bother me too much (yet). Maybe you could add numbers to brief sentences which carry foot notes, or add intended word count or page count for that section in brackets?
Your use of the term "backstory" sets off alarm bells. Are you sure that everything in your backstory is absolutely necessary for the reader to know, and if so, in as much detail as you present it? I'm currently researching for my next project, and I'm filling up notebooks with stuff I know isn't going to make it directly into my story, but they're things I need to know. Make sure you know what your reader needs to know as opposed to what you need to know. Secondly, once you've determined that you've whittled down your information to what the reader absolutely needs to know, the next step is to make sure it's presented only at that moment in the story when the reader needs to know it. This is likely the heart of your pacing issue. If you're laying out all of the details of your fictitious society at the beginning of the story, it's going to read like an infodump and many readers will likely fail to retain all of it for the point in the story when it becomes relevant. Finally, don't worry about length at this point. When I was writing the work I am now pitching, I became overly concerned about word count and at one point turned word count off so that I could simply concentrate on the story. When I had the first draft completed, I turned word count back on and began editing down. I especially recommend this if this is your first attempt at a novel. Good luck.