The manuscript I'm working on doesn't have a ton of dialogue. I would consider it a plot driven story similar to Cormac McCarthy's work, which is a major influence on my writing style. When I write, my sentence structure can be described as brief, clear, concise and to the point, which some people have told me creates an easy to read and simple book. When I try to expand my sentences I'm told they run for to long and need to be shortened to the clear concise format described above. Is there any right or wrong answer here? Or am I just over thinking this problem?
You want to have a book that is easy to read and is simple in a way. There is nothing wrong with your style of writing. In fact, it is proper writing. You will have a mixture of short to long sentences. Sentences do not need to run on for 20+ words when, like you have said, you can do it in less words and still get the point across. I would have to say you are over-thinking it. Sounds like too many people's opinions. Stick with what you are doing.
No right or wrong. When I took my first professional writing course, the prof told us to start writing with short sentences. It's the easiest way, and it works well. In my opinion, you should try and mix it up. Using short sentences over and over can wear the reader down. If you've ever read Henry James, he uses the longest sentences ever, and he's considered one of the greatest writers. Mix it up, write, rewrite, edit, until it flows nicely. Don't over think!
Very short sentences and fragments tend to speed up the pace; longer sentences slow the pace. Depending on the scene, use whatever keeps things moving at the appropriate pace. (Reading aloud helps you hear when things get too much either way.)
Good ideas, I think tinkering with sentence length is better saved for revisions instead of the first draft and I shouldn't write a long sentence just for the sake of doing it.
Have you read All the Pretty Horses? There are some great examples in that book of how varying sentence length can produce different effects. For example, the scene where McCarthy describes a train speeding past uses short sentences right before and after the train passes and one long sentence to describe the actual passing of the train.
shadowwalker makes a good point about reading it allowed. you could take it a step further and record yourself reading and then playing it back. it sort of gives you a different perspective on your work.
Use all sentence lengths! Understand how long sentences can affect rhythm and pace, and how combining them with short sentences and medium-length sentences can create the effects you want. If somebody says "Just use short sentences," they're limiting your toolbox, and limiting what you can accomplish in your prose.
I did some writing today and that is a great rule of thumb. I will remember that advice going forward and it helped me write more efficiently today and boosted my word count.