Injecting water into a rich a/f mixture is not a good idea

[Sampi]

Hi, I just installed Aquamist S1 system to my Audi A8 1.8T quattro 1999. It has a swedish BSR chip in it and it dynoed nicely 144 kW and 340 Nm last time.
Now I went to dyno again to check the effect of recently installed Supersprint catback exhaust etc. and installed S1 after that. 98 fuel is recommended with the chip, alltough I?ve been using 95 in daily driving. Well, I fueled the car with 98 octane pump gas for the dyno run and got LOWER figures from the dyno. Engine was running heavily rich (AFR 11-11,5:1,), S1-installer said that benefits of S1-system are seen only after AFR of 12,5:1. S1 brought only minor benefits when engine and room were hot. What could cause that overfuelling? Ofcourse S1 shoud be adjused with progammable chip to make it more usefull, but could that gasoline hassle be the cause of ECU?s eratict behaviour?