This paper aims to optimise the dimensions of Suction Embedded Anchors (SEAs) by investigating the opening mechanism through numerical large deformation finite element (LDFE) modelling. Consisting of two hinged half-cylindrical flukes, an SEA anchor uses a tactical design to allow the flukes to open under preloading to achieve more bearing area and, thus, a higher holding capacity. However, the applicability and practicability of this anchor depends on the opening process, where a critical dimension is the ratio of the anchor height relative to the diameter. A longer anchor increases both the forces prompting the opening process and the forces resisting it. The initial prompting force is the friction along the flukes and pressure on the wall annulus, while the initial resisting force is the soil pressure on the fluke faces. The LDFE results of this study demonstrate that these two components are in different orders of magnitude. Therefore, increasing the anchor height does not necessarily always increase the holding capacity but can have a detrimental effect on the holding capacity. The optimal anchor height is found to be ∼0.75 times the diameter. The detailed opening process and mechanism are demonstrated in the systematic LDFE analyses presented in this paper.