Attic Venting of Knee Wall in Cape Cod
The lower vents will indeed be less effective than the upper ones. In addition, you are reducing the effective insulation of the wall/roof in order to install baffles. With effective cross flow ventilation and a proper ceiling vapor barrier, you only need a total of 1/300 of the attic area in open free area ventilation. IMO, getting at least 1/2 this minimum area from the soffit is the important part. Actually balancing the areas when you have more than adequate ventilation is less important.

If you can achieve this 1/2 minimum area in the upper soffits alone, then forget about the lower ones all together. Only if you have no choice would I attempt to bring in air from the lower soffit. I'm fairly dubious on just how effective these would be.