Just my own maths and thoughts on that:
1) 4 pot 2 Litre engine makes it 500ml per cylinder
2) at 14 bar that leaves cylinder capacity at 35ml at full compression
3) at 18 bar the above is 28ml
4) that leaves difference of 7ml per cylinder = 28ml for all 4 pots
I expect (nearly) all oil present in the cylinder to burn on every stroke, I do not know if this assumption is correct, but if it is - after 600 revs (1 min of idling) the engine would have burned 300x28ml=8.4 Litres of oil
As I mentioned before the above calculations are based on my (limited) knowledge and few assumptions, but it provides food for thought...
Don't forget that you will get a lot of adiabatic heating of the gases as they are compressed which will push the pressure up much higher than the theoretical figure you've calculated, which assumes the temperature remains the same.
One also has to wonder about the accuracy of the compression gauge. FWIW, The compression figures are even, which speaks volumes more than the absolute figure. IMHO
That tells me that the piston rings are basically sealing well, otherwise any wear would be uneven across the pots. I doubt oil in the bores made a difference, again, because there would unlikely be the same quantity in each bore.
It doesn't mean there isn't a duff oil control ring that is allowing the main rings to become overwhelmed with oil when up to running speed, which wouldn't show up when cranking.
Kevin