I understand what u r trying to say
but there is one issue: if they shape 50% of users on 4mbit.... u cant get more ppl in that 50%...
but what u meant i assume is that the amount taken to be in the top 50% will get lower and lower
but the same number of ppl, relatively will stay in the top 50%, it was just easier to get there
so say theres 300 users, half or 150 will be shaped
the cut off point might have been 300gb
now the number usage limit might drop to say 200gb the cut off point (as ppl try to avoid been shaped and so use less)
still only 150 ppl will be shaped... they just got shaped sooner and couldnt make it to 300gb ne more
however the cut off point isnt a fixed amount and will vary based on the total pool of usage
so as one person becomes shaped another may drop out of the category of been shaped cuz the overall average changed and they are now below it, whereas the other person got above it