This is what doesnt make sense to me.... In putting an extra drain in the exhaust side, you're allowing the oil to drain back to sump instead of 'pooling' enough to feed the intake side of the head, therefore creating a possibility of starving the intake side of oil. Doesnt make sense to me....
I'd say, that as bealy suggested, many of these failures are due to other issues, lack of overall oil capacity and poor supply being the most likely suspects.
Speaking from my own first hand experience, I can again say i havent had an issue with oil. I have a modified sump, extended pickup, external filter and cooler setup, that holds a bit over 7L of oil. My engine is mounted past straight up and down, it leans to the exhaust side slightly! (refer pic) Again, i've never had any oil pooling in the head, never even caught any in the catch can at all! A properly set up rwd 3s can be as reliable as it ever was in any factory application, its been proved time and time again.