Fair isle, like any slip stitch fabric, is “shorter and skinnier” than any produced using the same yarn colors in plain knitting, single bed. Cables also narrow the fabric considerably. Begin with tension set at least 1-2 numbers looser than usual, and make tension swatches large enough to include all cable variations. After the cable crossings, be sure to return the needles to correct pattern selection before knitting the next row. Do not pull the whole group out to holding (E), as the whole group will then knit the color in the B feeder, and you will have a striped “mistake” on the next row knit. Leaving any needles OOW in the knit will select the needle on each side of the ladder to come forward, knitting the color in the B feeder. This may not work for you in terms of how the motif is affected by the vertical line created. If ladders are required, the vertical line in the B color may be eliminated by canceling end needle selection (KC II), or by dropping those stitches before you cable (which will give you a bit extra yarn for those crossed stitches). Ladders may be also latched up if you like, but watch where those floats are going in the fabric.
Making your own cards: try to control the length of the floats. Pre-punched cards with lots of punched holes can produce areas to be cabled by selectively masking areas with tape (both sides of cards). Conversely, you may punch diamonds, squares, etc. in the center of other shapes that would normally have floats too long for FI, to produce a B feeder color area for cabling.
Like color, most often, needs to land on like color, so stitches need to move further than they would in a one-color knit. Reversible ribbed cables share the principle of like needing to land on like (knit on knit, purl on purl). Starting out with a single row punched card, mylar, or program repeat, with the card locked, provides a quick test for tension, keeping track of patterns, etc. There are many, so at least initially, cabling on a constant number of rows apart may help avoid errors.
beginning to visualize the crosses
another of my “quick reference – some to try” handouts