ok...
p = posts
h = helios
p25 = h250 = 1month
if they got ober p50 (h500) last month, then for their good activity, they only have to pay h200 next month sencre they proved to be active. this not only incourages posting (as your plan) but it also incourages to be active rather than 25 posts-good-bye, and come back for 2 days next month. ...i ...think