My change of mind is based on measurements that I have taken and observed on several woofer lines. What happens is that for most of these cases the on axis amplitude starts to decline before a frequency equal to a wavelength center to center spacing. Despite using wideband woofers, when you place them in an array they just don't have the upper frequency capability that a single driver has. Now you may be able to live with the ampliitude roll off of the array, in many cases as you can cross to the tweeters in a little earlier. But I would emphasize that one should measure their woofer line and decide if the amplitude roll off near crossover is satisfactory for their goals. I'm finding that crossing over below a wavelength c-t-c spacing works better for me. A target of half wavelength is what I'm suggesting but I really hope that one measures to discern their situation vs. just using a rule of thumb guideline.