I have never used the stuff, as it always is out of stock or really expensive, where did you get yours from?
I would have thought a bit like other no rinse products , if you make too strong a solution you will have to rinse well after, or end up with a nasty taste, ruined brew or maybe making yourself ill. If it's too weak I would have thought you simply run the risk of it not working properly.
I'm sure you will get some better advice from someone else on here. My only suggestion would be to use an online calculator to convert American measurements to UK, and rather than make up a big batch just use the calculator to work out what you would need to make up 1 litre as an example, while keeping the dilution rates the same.
I have no idea if that would mean it would become less effective, as you would be using a smaller amount than suggested , on a large area. I wouldn't have though you would rub into any problems, probably best to wait for someone else on here to offer a second opinion