In tetrahedral geometry, ligands approach between the axes (along cube diagonals). Now dxy, dyz, dxz point closer to ligands — they go UP in energy forming the t2 set. dx2-y2 and dz2 are stabilised, forming the e set. The splitting is inverted compared to octahedral. $Delta_{tet}$ = $\frac{4}{9}$ $Delta_{oct}$ because: (1) only 4 ligands instead of 6, and (2) ligands don't point directly at any orbital. Because $Delta_{tet}$ is small, tetrahedral complexes are almost always high spin. Tetrahedral complexes never show the kind of low-spin behaviour common in octahedral complexes. Pairing energy almost always exceeds $Delta_{tet}$.