sig data
----------------- =  0.6
  all tx data

   sig data
-------------------   =  0.6/0.4 = 1.5
 non sig data

x MB non sig data, 1-x MB counted sig data, 4*(1-x) actual sig data

4*(1-x)
--------- = 1.5
  x

1.5x = 4 - 4x
5.5x = 4
x = 0.727

So, blocks that meet the 1 MB counted threshold, would actually have 0.727 + 4*(1-0.727) = 1.82 MB