Performing vs non-performing articles

Hi All,

I have 22 articles, with over 53,000 words. Out of these , however, majority of traffic is brought by only 3 articles. Now starting to focus on how to get those other 19 rank better.

We have done following:

- Matched kw difficulty and volume, they seem to be same.

- Average content length is same.

- All on-page structures are more or less same.

- I am considering doing a detailed backlink audit. But one of the highly ranked article has just 1 backlink.

Question:

1. What do you recommend should be approach from here?

2. Is this normal to have only few articles (10%) rank ?

3. Should we focus on more content or just optimization?

Thanks in advance!

Look into article size? Are they all around the 2.5k word average?

Thanks for reply @https://www.blackhatworld.com/members/zinxpxbl.1117009/ . Here are some stats:
Avg length for top 3 ranking articles: 2338
Avg length for articles not ranking well (18 articles) : 2125
I have removed an outlier. We wanted to treat it as pillar post. Its length is 6800 words.

Doesn't seem like it'd be significant enough. Was just a thought.