I have been using 6 cups of water with excellent results for several cleanses. This was a measurement I came to a couple years ago after having read the Stanley Boroughs booklet. I got the following excerpt from the link you provided:
"If the salt water does not work the first time, try adding a little more or a little less salt until the proper balance is found; or possible take extra water with or without salt. This often increases the activity. Remember, it can do no harm at any time. The colon needs a good washing, but do it the natural way—the salt water way."
For me this must be the 'proper balance'. It might be something else for someone else.
I'm on day 8 today and I've gotten interesting earthworm sized mucousy strings after my swf, first time I've seen those! Kind of graphic, but exciting to see nevertheless.