Well I've just had a look at the new panel under white light from the projector and unfortunately it's hot-spotting...
I took a close look at the surface in sunlight and I can see sparkles everywhere..
I think the matt acrylic is suspending the alumimium particles and a proportion of them are probably very close to the surface..
It seems that the matt acrylic is not the culprit that's doing the majority of masking in the other panels..but is probably doing some of it..
There's one more thing I'm going to try..I'm going to apply a coat of pure matt acrylic over the top coat mix, and hope that it will give just enough masking effect to tame the hot-spotting..
Here's what the new panel looks like in daylight..
From left to right...
Dulux white reference panel..
Base coat: white.. Top coat: matt acrylic and silver..
White/Silver/matt acrylic..
The camera doesn't show that the centre panel is more of an off white..