They seem to have struggled finding upfare price points for Comfort fares. As noted upthread, for awhile earlier this year, they were charging absurdly high differentials to upfare from Main to Comfort. I checked historical fare filings on ExpertFlyer and they seem to have peaked around spring/early summer before retreating again. Basic to Main fare differentials have barely moved during that time typically running $30 - $50 each-way, domestically. Perhaps this will help them goose Comfort sales somewhat, but who knows.

Here's a few routes with example Main to Comfort Classic upfare pricing one-way.
January June Today
DTW-LAX +$110 +$150 +$90
DTW-MCI +$50 +$90 +$30
DTW-BOS +$60 +$150 +$50

The DCA-MIA poster child route started the year very high at +$150 and has been falling ever since. It fell all the way down to +$30 for Main to Comfort Classic sometime in August and has been there ever since even with introduction of Comfort Basic fares on route.