HI Tom
Perhaps you can rearrange the aquascaping in your tank a little bit so at least the ventralis have an overhang where they can hide during the day. These guys don't like bright light. A friend of mine had his group of 6 or 8 for over a year, they were under an overhang for most of the day, only came out during the blue-light-only phase. During those dusk-dawn times they were eating like pigs, even flake food! Actually, he has a PB Tang, a huge Foxface and several other large fishes in his tank, no problem. But he did not have a sohal, which is a class of its own in terms of nasty behaviour.
At one time he added a mated pair of marine Bettas to his tank, they immediately occupied the place of the ventralis, chased them out into the open water and within a month or two they all wasted away. So, please create some space with lower light levels.
good luck
Jens