Hi,
Actually, not using file system on a 4MB flash is more a recommandation on 7.51 version, as it may prevent the using of Air Vantage service (update over the air).
A&D area and file system are using the same flash area. The max size for A&D area for a 32Mbits flash memory is 768KBytes. You can’t allocate more for the file system. If you need more, you have to use bigger flashes.