Working on revised/edited version. Until then…
ERRATA:
1)Instructions for sole stitch pattern should be:
Small: (k1CC, k2 MC) x 8, k1 CC. .. 25 sts
Medium: k1CC (k1MC, k2CC) x 8, k1MC, k1CC…27 sts
Large: K1CC, (k1CC, k2MC) x 9, k1CC….29 sts

2)RESUME WORK IN ROUND FOR LEG - MC and CC - starting with 29 (33, 37) sts
Make lifted stitch between sides if needed to tighten join, working off extra stitch first round.
Pick up MC. Add 4 stitches to back of leg as you work first round as follows.

Small: Add 4 stitches to back of leg. K1 CC, (k1, M1, k2 MC), k1 CC, (k1, M1, k2 MC), k1 CC, k1 MC, work center motif starting with Row 1, k1 MC, k1 CC, (k2, M1, k1 MC), k1 CC, (k1, M1, k2 MC), k1 CC.
½ TS: 33; TS: 58

Medium: Add 4 stitches to back of leg. K1 CC, (k2, M1, k2 MC)], k1 CC, (k2, M1, k2 MC), k1, CC, k1 MC, work 9-st motif starting with Row 1, k1 MC, k1 CC, (k2, M1,k2 MC), k1 CC, (k2, M1, k2 MC), k1 CC. ½ TS: 37; TS: 64

Large: Add 4 stitches to back of leg. K1 CC, (k3, M1, k2 MC), k1 CC, (k3, M1, k2 MC), k1 CC, k1 MC, work center motif starting with Row 1, k1 MC, k1 CC, (k2, M1, k3 MC), k1 CC, (k3, M1, k2 MC), k1 CC.
½ TS: 41; TS: 70

This is what I’m calling a “back of envelope” or “napkin” pattern, not much detail and assumes advanced sock knitting skills. I knit size medium sock. Sizes Small and Large were not test knit.

Medium sock was knit with sport or DK weight yarn using 2.75 mm needles at a Fair Isle gauge in round of ~7 stitches, 8.5 rounds per inch (2.76 stitches, 3.35 rounds per cm). Sock has mini gusset and mock short-row heel. Three separate Fair Isle stitch patterns on instep, sole and back of leg.

Foot total stitches 50 (54, 58). Total stitches leg: 58 (64, 70)

Finished size medium measurements:
Foot length, 9” (22.9 cm); 1⁄2 circumference ball of foot, 3.75“ (9.5 cm); leg 1⁄2 circumference 4.5“ (11.4 cm);
1⁄2 heel diagonal 5.25” (13.3 cm); heel to top of cuff, 7.75” (19.7 cm). Stretch limited.