the larger the sample... the slightly better feel you'll have for a large screen finished product.
but i've also seen samples that were literally 'heaven'... a 'grand slam home run'..., etc... only to find myself more than a bit disappointed when i got a full completed big screen of it.
what very often happens is the brightness immediately jumps out us... and when the blacks and colors appear to be same or close... we are hooked in. and yet, some of the smallest differences can often lead to big differences on a full screen.
3-4K is a lot to hang on a 12" sample... speaking for me personally.