In my opinion (as a long-time amateur builder of mediocre speakers), that 5 degree phase shift you calculated is audibly inconsequential. And chances are by moving the voice coil of the woofer forward that 1/2", you just might make your speakers imperceptibly better.
Does 1/2" make a difference at 375 Hz ?
I own a pair of IMF Monitor Mk III's with KEF B139 oval woofers. The woofers are damaged and I was fortunate enough to be able to purchase a new (unused but 10 yrs old) pair of B139 woofers on ebay. Lo and behold, they are not identical to the originals I have. The diaphragm appears to be the same dimensions, but the frame is a different size and the mounting hole pattern is different. In order to mount these on my IMFs, I need to make an adapter plate. I can make this out of 1/2 inch MDF. The problem is that the front surface of the diaphragm will then be 1/2 inch further forward than the IMF design. By my math, at a crossover of 375 Hz, 1/2 inch is about a 5 degree phase shift. Is this 5 degree phase difference critical for the "time alignment" of the midrange and woofer ??
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