That particular decision I think came down to him assuming that the reason the Church Hussars weren’t committed to the field was because they were being held in reserve, and believed that he would be able to orchestrate the army from his position and might not even have to commit the Cuirassiers. As pointed out in-setting, Wulfram is a conventional man, and didn’t think that over four thousand heavily armored riders with magical weaponry were waiting in the forest to burst out at a moment’s notice.
Because, as pointed out in-universe, that particular tactic went past “unconventional” into “do you even know how horses work?”
Now, he should have expected something to come from the woods. And I’m guessing, if he expected anything, he was expecting partisans. If it was partisans in the woods, and there were Church Hussars committed to the field instead, Blogia would likely still have been a Tierran retreat. But not the utter rout it was.