What is the reason for tweeters wired out of phase?

When I researched replacing the SL2000 tweeters in my Monitor 5JR+ speakers I came across the Polk crossover diagrams. It shows the tweeters wired with the speaker's ground wire connected to the tweeters + and the speaker's positive connected to the -. Reverse polarity from the woofer. Sure enough, that's just what I found inside. So I connected the new RD0194 tweeters just that way. Sounds great. Okay, I know, if it ain't broke don't fix it, but why the polarity change? What does this do? Also, if I plug in the crossover values for a 1st order filter (just the one inductor in series) using 8 ohms for the MW6503 woofer and 0.65 mH for the inductor I come up with around 2,280 Hz which seems reasonable. But the tweeter's 2nd order filter with 8 ohms for the RD2000, a 12 µF capacitor in series and 0.19 mH inductor in parallel just doesn't seem to work with the usual online X-over calculators. A Polk revision of the crossover for the SL2500 tweeter uses a 13.5 µF capacitor, and the same 0.19 mH. What's going here, any ideas?