Weakness of the triceps surae muscle can call upon many of the other plantar flexors of the foot, the Peroneals included.
This will facilitate the muscle an its other functions such as eversion. Eversion is linked to pronation of the foot, and if the Inverters of the foot are weak/inhibited, foot posture can be compromised.
-> Look out for eversion when asking only for dorsiflexion
-> Look out for this in patients who pronate in stance phase and evert in swing phase.