The Necessary Existent does not depend on another for existence. Bodily magnitudes, parts and determinate states raise precisely the questions of limitation and specification that characterize contingent existence.
لما فيها من شائبة الحدوث والإمكان
Because they contain an aspect of origination and contingency.
A particular body's size, shape or location invites the question why that determination rather than another obtains. Such specification is treated in classical kalām as requiring explanation; God’s necessary existence excludes this kind of dependence.