Hmm, pretty good question OP.
 
According to my opinion, merit should not belong to lengthy postes or topics. Rather you should emphasize your knowledge and explain it. It means that a large post does not attract people, you have to explain the big meaning in small words. 
 
My personal opinion is that quantity is not quality. I am putting in front of you some of the rules of the post, which in my opinion, has caused me to get merit. Which you can also implement and post quality better. 
✔. Explore new knowledge as much as possible and explain it in easy and simple words.
✔. Do not hesitate to ask high-ranking members in any thread, whatever you want to ask or explain within the scope of the principle, you can express it through a clear-cut post. 
 
Advice: IMHO, you should just focus on post quality and not merit. If your post quality is better, then you will definitely get merit.