I suppose I don't know what I mean by the sentence-length average being low.
Yes, they compare to a body of work and to individual authors.
Mathematically, my sentences average out to around 9 - 10 words per sentence over the entire piece. I have very, very few sentences with more than thirty words, in the entire novel. Most novels have occasional sentences that are 40 or 50 words. The opening sentence in
The Fault in our Stars is 42 words, for example.
The program states that in fiction, on average, sentence length averages often fall between 11 and 17 words. (Again, as an average--length variability is a different analysis.) So, the program points out that my average falls short of what 'the industry' more typically publishes.
The graphical output on this analysis is useful -- the program provides a bar chart of sentence length, in order by sentence, so a person can spot areas where prose threatens to get choppy. (Which might be intentional, or might not be intentional.) It's not uncomoon for me to spot areas where I have a run of five-word sentences, for example.
In contrast to average sentence length, my length variability (and structure variability), appear to be great. It's just the average length is low. So, I've been targeting areas with runs of low sentence lengths and asking if there are obvious re-wordings that might increase the complexity and average length without losing clarity and flow. Here's an example of such a run from the chapter I'm working on:
Ethyl’s brow wrinkled in thought. “Is that your concern?”
Celeste gave a half-hearted shrug. That and a dozen other things.
“If it’s that, why don’t we build a residence behind the inn? The property’s big enough. We’ll put a cottage there. A caretaker’s cottage.”
Horrified, Celeste whispered, “No. Then I’d be leaving my home each night, while strangers run loose. Don’t you see?
Average sentence length there is 6. The prose is clear enough, but the program is right--most of those are under ten, and it could get choppy real quick.