It seems that your Symbiosis flash is slower to ignite if you use a higher power setting.
You might want to try four things:
1) Check from the camera menus whether you have set the flash to sync either pre or post curtain. Selecting pre curtain should give a longer reaction time window for the flash.
2) Try using a longer exposure time. You could try to find out if there is any correlation between the exposure time and maximum usable Symbiosis power setting.
3) Try it with a fully charged battery
4) If you purchased the housing and strobe from the same local dealer, ask for their help. However, if you mail ordered from different sources, you are on your own concerning compatibility issues.