PamSmith, I think you should be using a mesalamine enema, not a cortisone one. The cortifoam will not give you a lot of coverage in the sigmoid colon; I think it is a pretty small dose of medication, effective primarily in the rectum. I may be wrong, though - it's been a long time since I used it.
I don't think the different brands of oral mesalamine offer anything new in terms of efficacy - some of them might be better for you if you have trouble remembering a midday dose (I think the Lialda, and the Asacol HD, are only twice per day).
Your dose of oral mesalamine is pretty high for someone with disease only in the sigmoid colon. The rectal mesalamines will treat that very effectively. Please talk to your DR about prescribing rectal mesalamine retention enemas.