Hi Norman
Sorry, I can’t offer anything specific to this problem as I have not had my hands on the particular housing you have (or for that matter, the camera).
From your description, it sounds like the housing has a refractor to re-route the flash slightly, and then the light passes through a diffuser. Perhaps this loses some of the flash light level, but the camera should be able to compensate for a small loss anyway.
One thing I’ve found with the very small Sony cameras is it is quite easy to accidentally put your finger or part of your hand over the flash when holding the camera. I would be surprised if this was happening to you with the camera in the housing, especially as the results appear quite consistent, and I’m sure you would have noticed if you were blocking the flash with your hand!
When you took the example shots, especially those that included the other divers, did the flash appear to be firing correctly? Did the divers in the pictures notice the flash going off? If not, then perhaps there is a problem with the flash refractor or diffuser on your housing.
That’s all I can think of I’m afraid.
good luck
Graham