The uri has two appearances in Suricata: the raw_uri and the normalized uri. The space for example can be indicated with the heximal notation %20. To convert this notation in a space, means normalizing it. It is possible though to match specific on the characters %20 in a uri. This means matching on the raw_uri.
The raw_uri and the normalized uri are separate buffers. So, the raw_uri inspects the raw_uri buffer and can not inspect the normalized buffer.