A greater positive charge means the ligand is strongly attracted and pulled closer, and thus it creates a stronger crystal field. The potential energy value of the barycentre should thus be higher, since repulsion experienced by the d electrons is stronger. Why is though the value of the Δo increased - the potential energy difference between the various differently oriented d orbitals? Each orbital experiences stronger repulsion if charge on metal ion increases and the ligand is pulled closer, but how can anything be said of the energy difference Δo? Both t2g and eg are at a higher level, that's all.