My hunch. The plastic fingers pointing up will reduce splash when our urine hits them first time, but if the bottom of the urinal is flat, the plastic will stick to it causing the urine flow to be slow, and due to capillary action, the urine rises above the fingers and causes splash again a few seconds into our urine passing.

If the fingers are pointed downward, the urine seeping through the downward fingers can flow freely to the outlet, and causes less splash with the urine rising through capillary action. The holes on the plastic layer will anyway avoid the urine splashing when we point our pipe against it.