I have used this AI in other mods. Sometimes it needs a little help to get started. Don't take advantage of it and use a unit of light cavalry to attack then withdraw. Once engaged the AI will sort itself out, form up properly and counter-attack.
Edit- this is a vanilla issue not the UAI's fault, but this fix works quite well with the UAI
Try to resist the temptation to pound it with artillery while it is confused. Well worth it for a decent battle (okay, so I can't help myself sometimes )