In Magee, it says correlated postures for lateral tibial torsion is toeing out and excessive subtalar supination and the compensatory postures are excessive subtalar pronation and functional forefoot varus. Shouldn’t be functional forefoot valgus? Because when I do it I feel its valgus. Pronation is eversion and supination is inversion, right?

While correlated (or associated) postures often accompany many pathological presentations, the compensatory postures are usually opposite in direction to the pathological presentation. Firstly, you are correct in your observation that pronation of the foot/eversion and supination of the foot/inversion are related.

However, you should bear in mind that even though no such anatomical division exists, the foot is functionally divided into a fore foot and rear foot (sub-talar) regions and these 2 parts work in opposite of each other to keep the foot balanced, or if you like, in a state of ‘functional equilibrium’.

Therefore, by way of the above, rear foot (subtalar) supination is compensated by fore foot pronation (or valgus) while rear foot (subtalar) pronation is compensated by fore foot supination (or varus). This corroborates Magee’s observation.