The requirement for rank increase varies, and can depend on these factors:
- Post count : how many topics and posts have you created ? OK, admin explained this expressed in numbers.
- Karma : are your topics and replies getting positive karma? How much positive karma is needed per rank, is there a number? how does negative karma affect this, in numbers?
- Online presence: are you present on the forum often, or just logging in posting the out. OK, I assume that the time spent on the forum counts. But how much time, does it have any relationship with the number of posts and how is it calculated?
- Registration date: when you signed-up, to prevent cheating with ranking. I'm not sure I understand this. But it doesn't seem like a crucial factor to me, if you look at the time spent on the forum as well as the deserved karma
Based on everything, it seems to me that the decision to enable the forum account upgrade is made manually and depends on the administrator's assessment. Which is completely wrong.
You have raised good concerns, it might be a little bit hard for us to calculate the activities, on these factors, because number one there are so many, and 2nd there is less information about these factors. If the admin had explained them well, then we might have been able to calculate our activity with no error or ambiguity.
But at the moment, I think this is all, and at least it works, and helps a little bit in this situation. Talking about your questions, I think, the online presence and the registration date, have the same logic, for example, 1 day will count as 1 activity with 1 post, (on BTT) but if you have been registered for 15 days with no post and then make started to make multiple posts in a day, the activity will increase. Like if you make 15 posts in one day after 15 days the activity will be "15". I think the same logic is here for the last two factors.
Talking about karma and post count, I assume admins must have some formula set to count activity.