The area most cam companies error on is the exhaust. This causes problems with these limited intake designs. The exhaust VE's are the most important on these setups.
Simply put, on an N/A motor the intake aircharge is not assisted.
After the combustion stroke there is tremendous pressure in the cylinder. As soon as the exhaust valve cracks open it flows a LOT of air. It's basically boosted out of the cylinder if you want to look at it like this. Having the exhaust valve open too early not only costs heat (power) & velocity through the exhaust runners, it also empties the cylinder before the intake valve is open enough to take advantage of the pressure differential. (in a limited overlap/smogable camshaft this is especially true) This causes exhaust reversion & is one of the key factors in surging problems. By the airflow reversing course it is loosing a lot of it's inertia.

By retarding a reverse split cam, you take advantage of the long-runner intake (torque gain), yet still get excellent peak power.
Retarding the cam opens the exhaust valve later, resulting in hotter exhaust gasses & therefore more exhaust velocity, which helps scavanging.
Another thing to note is most advanced cams open the intake before TDC. The intake airflow needs vacuum to fill the cylinder. Before TDC the intake air-charge is relying on exhaust scavanging to pull the air into the cylinder. On car w/limited overlap (smog grind) there is very little scavanging thus the intake air-charge really doesn't start to fill the cylinder till ~10 degrees ATDC. By retarding the cam, the intake will open later....waisting less intake lobe.

Increasing the exhaust flow (more exhaust duration then intake) will cause the engine to evacuate the cylinder too quickly causing the exhaust gasses to stall in the header & be drawn back into the cylinder during overlap....Reversion, mainly in the low-mid range.

By retarding one of these exhaust bias cams you can minimize the effect of the exhaust lobe....open the exhaust later & it won't stall & get drawn back into the cylinder. Effectively increasing cylinder pressure (power) in the low-mid range dramatically, + extending the upper RPM capabilities of the cam.