The present work is a contribution in analyzing dimensional deviations in ellipsoidal thin-layer steel heads used for high-pressure air brake reservoirs. The dimensional deviations are attributed to the thickness distribution during the drawing process with regard to input geometrical parameters such as punch and die diameter, and also die and punch fillet. The aim of the present work is therefore optimizing the input data in order to respect the initial geometrical requirement. Investigation has been carried out using FEM code Abaqus, on a case example produced by the Algerian truck company according to G.R.C E81-102 standard. FEM simulations followed the process of deep drawing and concerned the effect of the most influencing factors such as the die corner radius, the punch corner radius, and the blank radius. Dimensional deviations are analyzed in terms of variations of thinning along the true dish path and hence engineering models of the corresponding true strain in the straight zone, the knuckle zone, and the crown zone of the dish are proposed.