This is an age-old subject, but I see that a lot of speculation is going on about "back pressure" in the crankcase being an issue - I don't think that is the place to look.  I don't think the location of the vent discharge as it relates to the pressure (or "suction") exerted has any effect.  The blowby flow rate is created by the leakage across the rings from the hundreds of psi of combustion pressure so a few inches of water change in pressure won't have any significant effect on flow rate.  I think the biggest effect on oil entrainment is the internal engine design and we can't change that.  The next closest part to the engine is the vent hose as it comes out and I think that should have an up slope and be as large as possible to keep the velocity of the gases down, allowing oil to drop out and run back down into the engine.  After the tube turns back downhill there is nothing you can do, as the oil will run downhill regardless.  Rerouting might change how much of the oil is deposited on the belly, but it won't change to total quantity.  I'm trying to figure out some sort of aerodynamic separator to keep the oil away, but I'm not sure there is such a thing - too much turbulence down there.  And do oil separators work?  I have no experience, but the on-line comments range all the way from "perfect" to "not at all".