Increasing oil consumption running running over square is due to increase in BMEP (brake mean effective pressure) While theoretical, when you develop the same horsepower at lower prop RPM, the duration of the combustion stroke is longer creating more time for high pressure to act on your rings. Oil expelling from the breather pipe indicates your rings are worn or ring end gaps are too large or incorrectly installed. You are not developing higher pressure so much as you are giving the pressure more time to act on the rings. At higher rpms there is less time to act and the oil control ring wipes up excess more quickly. On a high time engine or one with worn rings you may see more blow by into the case pushing oil out the breather. Given that most aviation engine oil sumps are over serviced for most missions "breather topping" is not uncommon and can be aggravated by more blow by. Simply put there is nothing free. Run over square and you get better range as more heat value of the fuel is directed to the propeller and not out the exhaust pipe and heating your engine heads. The flip side of that is your rings are under combustion stroke pressure longer and your oil control ring does not "swing the mop" as fast.