A story, and alot of questions

Here is another technique that I use on the 21SE that seem to get the sails trimmed correctly and is almost identical to the 18. This is taken out of the book Catamaran Racing for the 90's.

Adjust the jib traveler until both the upper and lower tell tales on the jib break at the same time. This means when either stalling or luffing the upper and lower telltales break at the same time. Once you have set the traveler and jib settings you trim the main to the upper most telltale on the main.

You essentially sail by the upper and lower telltales on the jib and the uppermost on the main. These should be breaking generally in unison. If not, start micro tuning all the adjustments. Then once set you mainly sail by the lower telltale and only checking the others to make sure you have everyting trimmed correctly.

Sure, i have been sailing my spin every weekend for a few years now...
my suggestion is "reach more"

i think if you just fall off and then point higher (never in a straight line) you should be able to get your apparent wind to move forward and then back off a little again.. you should be able to controll it more and have it collapse less..

I found I was doing the same, did the same as above. Found I was also over sheeting the spin to gain ground which was hurting airflow across jib and main.

Are you falling off when the luff starts to collapse? How hard is your luff? Sometimes it all feels right and other times it just doesn't, I really think it is in the set. If the tack and halyard are not tight to the pulley the sail doesn't perform correctly. I may need to mark my lines to show proper set and stop guessing.

yes i fall off when it luffs (or sheet in).. i play the luff curl,... i let a small curl form and then i either fall off or sheet in a tad to get it to un-curl...

different cuts/spins perform slightly different, but you always want a fair amount of luff tension on any sail.. most cats put some pre-bend in their pole to establish the correct amount of tension

I may be running into an issue with the block placement as I can sheet the spin tight to the block. Gonna change my sheets to what Karl and the Wildcat are doing, currently I sheet to the eye splice wrapping. I also pre-bend the spin pole and have a hard luff if set correctly. I may need to raise my tang and bail as well, the sail sits low and I can barely see under it.