The Hamiltonian three form plays the role of the generator of the conserved quantities w.r.t.the corresponding displacement vectors. It is not uniquely defined up to a total differential term, the Hamiltonian boundary expression. The meaningful concept of energy is always the difference of the value of energy w.r.t. the reference so that we do not have a unique definition of the physical energies. For the covariant Hamiltonian approach we introduced a suitable boundary expression [PRD 72,104020] and in recent works [PRD 84, 084047; GRG 44, 2401] we found satisfactory results obtained from matching the four metrics on a two sphere of for spherically symmetric spacetimes. Here we analyze the general 4-D metric matching on a closed two surface. We find that for a two surface which satisfies isometric embedding into Minkowski space, there are still two degree of freedom remaining to determine the choice of reference. If an optimal choice can be found we then get our quasi-local energy value. This is a joint work with Chiang-Mei Chen, James M. Nester, and Gang Sun.