So here is what has worked for me with long runs and pulling back with weeks and long runs. Others may have their own way, this is the one I use, but it isn't exactly original.
I alternate between two types of long runs.
One week I will simply run for a set amount of time, all of it easy running. On these runs, I will hydrate as necessary, but try not to take in any calories before or during the run (this has been a hot topic in other threads). The theoretical purpose is to get the body used to going for a long time, and to get the body to store my glycogen and burn fat more efficiently by letting the glycogen deplete during the run. I top out at 2:30 or so for the duration (my marathon time is lower than that)
The next week, I will go progressive, but definitely shorter (usually 16-18), starting easy and slowly turning the screws such that at some point in the second half, I hit marathon pace and then put in the last few miles at faster than marathon pace. These are the hardest workouts I do, and take the longest to recover from. I also try to wear my marathon shoes, and take gels, etc like I would in a race.
As far as tapering the long run back before the race, I shoot for this basic model (from Pfitzinger?):
3 weeks out: 20 miles easy
2 weeks out: 17 mild progression
1 week out: 13 easy
If you are asking about taking down weeks in training, I do that also, but it doesn't affect what I do with my long runs. It affects what I do the rest of the week. I try to do 2 or 3 weeks up, then down by 10-25% for a week. I think it has helped me stay healthy and keep from burning out on solid mileage for weeks on end. It also gives my body to absorb the workload and make the adaptations necessary to race faster.
One comment I would make is that you should develop a more distinct purpose for your long runs. Most of what I have read recommend either doing long runs that are about 1 minute per mile slower than race pace (on average, adjusting for terrain, weather, etc) or that involve some sort of progression from easy to marathon pace or faster by the end (simulating race feel). It seems like 30 seconds per mile slower than race pace might be too fast for the easy long runs (thus your inability to feel good finishing a 22 miler) while not fast enough at the end to really simulate race conditions.