Take this with a grain of salt, but I had a terrible time getting an A&E FP last October, and this is what someone told me...
During the busy summer months, there are 2 sets of sisters meeting during the day. Once the slower fall season hits, this is scaled back to 1. Couple that with shorter operating hours (as well as several nights of early closure due to
MNSSHP), and there are far less FPs to be had in September than, say, July, making it a much more difficult FP to obtain during a slower time of the year.
To up your odds, try to get A&E as late in your trip as possible, and try for overlapping singles if you have a larger party. The dibb only shows availability in blocks of 4, so there could be many 1 or 2 person openings still out there.
Also, as PP mentioned, people staying on property for 5+ days are already scheduling those days. By scheduling as late in your trip as possible, you can tap into days that the least amount of people have had access to already.
Finally, if at first you don't succeed, keep searching as people change their plans all the time. A&E hoarding is as common as ADR hoarding these days, so you'll likely be able to find availability the closer to your trip you get.
Additional slots are unlikely to be added unless park hours are extended later on.
Good luck!