I'm not sure if I entirely agree with your formula with respect to guild support.
I was doing some beginning cooking, and making orange juice.
I had no problem getting skill ups when I had skill 8 and 9, and paid guild support. I didn't get any more skill ups once I hit skill 10 (though I admit I didn't do many, as I moved onto other synths).
As orange juice has a cap of 10 according to this site, then as I don't think I was on a special day, then I should have been in the redundant zone, but was still getting skill-ups.
This theory becomes much more evident at higher levels.
Bellow level ten, I would say just pump out whatever recipe you can succeed at, but when you are approaching 60, and on average need 30+ synths to make one level, this formula could help you do it in 24.
Plus since you can't give any day, moon, direction facing data for your crafting at level 8 and 9, you could still have gotten yourself back out of the redundant zone by being in Darksday, and a new moon, not to mention the direction you were facing, wich likely was somewhat random.
If you have 10 levels of cooking to base this theory on, you need to work on a few more crafts, through some of the harder skill zones, and then I will be more then happy to see what you think of the formula.
Does anyone have any more information on this? To my knowledge I have never skilled on a fail over 5 levels (6+) away. I was considering it was more of a gradual scale, as opposed to an abrupt cut-off.
Recent Threads (Eruntalon) and past info (41.1 = 41.9) show that SE favors abrupt cut-offs.
Also, can the "skill off fails" be altered in the same manner? I.E. Day + moon..
I was under the impression it was based upon base skill.
The 5 level gap maximum to skill up on fails is nut an "X" value. It is just a solid calculation between recipe cap and your current skill (including guild items, I would believe). I will add a note to that section to maybe clear this up.