With the Spanish model, vadThreshold has to be set much higher (as above, something around 4.0 to 4.3). You should turn Rejecto off and find the ideal setting for vadThreshold first, and then use Rejecto to exclude out-of-vocabulary speech that remains. This isn’t an accuracy issue, since there is no way to be accurate with utterances which aren’t in the vocabulary – they are simply unknown. This is a combination of oversensitivity and out-of-vocabulary recognition, for which vadThreshold and Rejecto are respectively used.