Why would low lift head flow hurt power?

273 said
Why I ask
Cause what I take from Al Noe statement is it seems they go out of their way to keep low lift flow numbers low.

If you compare older AFR airflow charts against same year competitors, the AFR seemed to have better flow numbers across the board. As the competition improved so did AFR. Now the low hanging fruit is easy to pick but as that is cleaned up the rest gets increasingly more difficult to get to.
On any project you need to determine you goal and stick to it. Generally a race port on a street engine that sees a maximum of 6500RPM is not going to perform well. The 70 Boss 302 is a prime example as the intake valves were huge for street and the ports also. On the race track with the engines turning 6500 to 9000RPM they worked well, but getting a car going off a stop light they felt sluggish. Once up to 3500 RPM they came alive. For 71, Ford reduced the intake valve size a bit. The 2V Cleveland heads had a large open combustion chamber with poor combustion qualities but smaller ports. CHI in Australia combined the smaller ports of the 2V heads with the smaller quench combustion chambers for Boss, Cleveland and Clevor engines. Ford of Australia produced 302C and 351C engines for a number of years.
For a street engine using a cam producing up to 0.550 valve lift, low lift flow is of primary importance as the valve is not out of the valve/seat curtain flow controlling range for long. At lifts of about 0.350" to 0.400" and above the port becomes the limiting factor. With this in mind, high lift flow is important but more consideration should be devoted to the valve diameter, the seat profile and the angles on the valves for the average street engine that sees occasional track use.