But a 5cm strip on a mudguard (like in that picture) isn't visible from all directions, which is part of the EN standards. It's not just 25 square cm of reflectives.
It's not just for people coming up behind you, it's for people coming up to junctions at side roads, infront of you and off to one side, etc.
The problem with this line of thought is that, for example, people coming up to junctions from side-roads will not hit you with their headlights until you are literally in front of them (and nobody coming up to a junction is looking there, rather they look to either side where they expect to see traffic). Of course, that's simply a fundamental problem with all reflectives, not with their position on bike/body, and a good illustration of why lights are more important.
I was once almost caught out by a rider who had pretty much a full luminous body suit on while driving round a right-hand bend. Of course my headlights were hitting the verge, and there was nothing to indicate he was there at all except the faintest of bobby-dodger red LEDs. Sure enough, when I straightened up he blazed into life like a lighthouse. Good job I wasn't doing 60mph though
Anyway, to get back to the point at hand, reflectives on the mudguard are at the perfect height and also maximally visible to the traffic which is most likely to nail you. After all, on an open road ultra-distance ride, probably 99% of vehicles interacting with you are following on, and I'd have thought over 99% of accidents too (there can't be too many junction crashes or head-ons at night when your lights are so obvious).
That's not an argument against adding extra reflectives or extra lights, because you never know when you might be the one to get tangled in a freak incident, and it's quite understandable that people who're afraid want to do anything to feel more comfortable. But I think it probably is an argument against *mandating* extra stuff that isn't likely to make any difference.
Recumbents are a different matter as the PBP regulations say that they should just make suitable use of additional reflective material as any gilet/waistcoat would be obscured:-
"
If your reflective gear is obscured (perhaps because you are carrying a backpack or riding a recumbent) ensure you have additional reflective material to ensure you are visible
"
Yes, but the downside is that this is subjective again. You chaps can simply provide a basic EN-compliant vest and there's no way they can refuse - after all, it's specified in their own law.
As soon as you have a subjective value it becomes troublesome - remember that some people would argue that no amount of reflectives make a recumbent visible. Come to Edinburgh and go for a test ride and you'll find a neverending stream of snivellers to tell you so (curiously, never motorists though - only cyclists have trouble with it).
And that's the thin end of the wedge, next you're onto the stupid flags, and it all gets a bit awkward when you point out that if you can ride through capital city winter rush hour without any trouble, you probably don't need to take emergency precautions to ride on a quiet back road, and yes, you're considerably higher than the lane markings we're navigating by...
bah!
</rant>