If I remember correctly, most of the "flavoured" yoghurts in the shops also contain gelatine as a thickener. So be careful if you are comparing against them. I could be wrong here though, correct me if so.
I think andiesenji's advice is spot on. We've also made the Easy-Yo yoghurts at home, and tehy always perform and stated below, and I think the plain one is even FAILSAFE for us. The time in the thermoflask is quite often the indicator of set or not set for us.
Russell.