We don't have synonyms for isocephalism yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are isocephalic and mesocephalism.
(n) :
(art) A peculiarity in the design of bas-relief, and also in painting, in which the heads of human figures are depicted at the same height from the ground, or along a vertical line, regardless of their pose.
(n) :
(art) A peculiarity in the design of bas-relief, and also in painting, in which the heads of human figures are depicted at the same height from the ground, or along a vertical line, regardless of their pose.