The pieces on my car definitely look different, with the most notable difference being that there are drain holes on both sides of the divider. Only 2 on the passanger's/right side (US) of the divider and at least 6 on the drive's/left side of the car. I would take it apart again to verify where the water would go if you were to add drain holes there. Seems like an odd setup for stock. My car, a US 2009 would not be capable of having the water issue (unless the holes were blocked).
That may be an aftermarket cowl, that someone replaced - because they broke the old one when replacing the windscreen???? I too never had an issue with water pooling there, unless it was stopped up with leaves and debris. That would be a common sense issue while engineering the car. IMHO; dumping any liquids directly on top of the ignition coils would be a major faux-pas and can cause intermittent misfires when the current gets discharged into the spark plug well walls instead of the other end of the spark plug. Just my 2-cents....
Yes, aftermarket cowl makes much more sense... would be interesting if more of those who drive on the wrong side can chime in and say what their parts look like (and if known to be OEM and what year).
LoL; "wrong side" LoL; as you stated, they are right drive in Japan..... so that problem shouldn't exist - unless they wanted to give the "middle-finger" to the imperialist UK. More than likely an aftermarket part that missed the weep holes when the OEM plastic was scanned. It takes real effort to perfectly duplicate a part.
Have you got a picture of yours PrimalPrius? That'd be interesting to see! My dad owned the car from new. If it was an aftermarket part someone slipped it in without say anything to him about it. It was serviced by Toyota for most of its life too. With that said, it's a 2005 model. He bought it before they were popular in the UK, so maybe Toyota addressed the issue in later models. I could drill some more holes on the bottom, I think that would be safe if they're towards the back but I think the 3 I drilled should be enough. Looking at the design, with the bonnet closed I'd say 90% of the rain will drain off somewhere else.