Thank you.
I took the liberty to re-create your crossover in
XSim using my first attempt to do speaker measurements based on
Udemy course. I do indeed see a dip in frequency response when I change polarity of top woofer!
Please don't judge me, I'm having way too much fun learning! Attached is XSim project archive with the original crossover and Dennis Murphy's mod. Have fun playing and understanding how it works! Adding another 6.8 uF capacitor in parallel with C3 4.7 uF seems to get a nice slope reducing speaker brightness.
View attachment 219404