Some pages are the same size, but the page has much better engagement - maybe they use engagement group. If you want to increase the amount of engagement, you might consider using engagement group. About content, If you use repost stretegy - In my opinion, you should choose posts that have been posted a few months or even 1-2 years ago. Because, for new content, there may be pages larger than your page that have been reposted first - this may affects your engagement (No one wants to interact twice with the same content).