Well my supply voltage in the workshop is consistently above 250v, last time i checked it was 251v but I've seen it over 253v regularly!
Anyway, setting the 'standard' voltage at 230v means design output in wattage will be reasonable at the lower and higher limits, if the old UK standard of 240v was still in use, then our appliences would not be as efficient on the continent.
IE, The Carver Fanmaster is rated at 230v and oddly at 1850W heat output, but that's actually a nice round 2000W at 240V, in this country then you get the full 2000W, or better in my case, but abroad 1850W or less.
Truma's equivalent Ultraheat is rated at 230V and 2000W, that's nearer 2250W here but what you pay for on the continent.
Little of this applies to amperage drawn then, you still draw the same amperage regardless of the available voltage, only the work done, (energy produced), varies
The good news about lowly 6A supplies is the available overload you can make use of , most 6A breakers take a controlled overload. the most common 6A'B' breaker can take up to 1.45 x 6amp for a useable time.
IE, you can for instance leave 1kw of heating on and still boil a 2kw kettle, that is, if you don't over fill the kettle so it boils and switches off before the overload time is exceeded.
It's a pain at first but you soon get used to it!