Potential for Mukuyu-1's Results to be Above Market Expectations, page-18

I think you may be getting mixed up between overbalance (difference between mud weight and pore-pressure), and over-pressure (difference between normally pressured aquifer and HC's). Apologies if I've got this mixed up but owing to the large difference in pressure gradient of the mud compared to HC's in pore space, the overbalance will increase with depth for a single column (orange lines in plots). It will increase as well for two columns that are offset by a (relatively) small amount (green lines), but overbalance could decrease if the pore-pressure increases significantly from one sand to the next (Yellow lines).

TLDR: It could be two columns or one, not enough information to know at this stage.