I see a different value from @ddmrddmr dashboard in the "Merit per Post II (Chart)" tab.

Probably, the difference must be from the account of deleted posts.
Yep, huge amount of old deleted posts in Russian board was the cause of that heavily inflated merit/post ratio. That's the main reason why I switched to ninjastic.space when it comes to counting posts and calculating merit/post ratio as month after month Russian board had the same issue.
I had a memory of that.
I think I will stick entirely to Merit Dashboard, I haven't the energy to juggle between two different sources.
Thanks for the clarification!