Catamaran sails are always high aspect ratio, low draft, draft forward sails. These are designed to be sailed with less twist. If you trim off wind by centering the traveler at all times and then easing mainsheet to stop luffing on the lee side of the sail, your sail will have excessive twist for it's design. Monohull sails are typically cut for this type of trim, but then what choice do they have? The traveler on a monohull is very narrow compared to a cat's. This is regarded as one of the catamaran's other chief performance advantages over the monohull besides righting moment, that is the ability to pull straight down on the mainsail when off wind. This is due to the traveler track being as wide as the beam, and of couse the skipper has to use this width by easing the traveler out from center and sheeting the mainsail straight down. It only makes sense. I can refer you to any of several well regarded texts on sailing written by great and well-known sailors.
With no spin - I agree - traveller further out - you don't want too much twist. With a chute the apparent wind is so far forward there is no need to travel out (unless it's really light) and only minimal twist is required which can be supplied by slightly easing the sheet vs. upwind. In either case (spin/no spin) I'd just set up the sail to keep the tell tales happy at upper and lower luff and the tails off the leech streaming with the occasional curl to leeward.
Traveling down too far with a spin will pinch off the slot between main and spin. It's a good way of temporarily depowering the boat if you need to correct a problem (e.g. cleaning weeds off the boards or rudders). Just oversheet the spin and travel down and the boat will slow right down.
