When piece measures approx. 16-18-20-22 cm from marker on heel (= approx. 4-4-4-5 cm remain), insert a marker in the mid of each side so that there are 22-22-24-28 sts both on top of foot and under foot.

Make this lower case.
when piece measures approx. 16-18-20-22 cm from marker on heel (= approx. 4-4-4-5 cm remain), insert a marker in the mid of each side so that there are 22-22-24-28 sts both on top of foot and under foot.