How tight should the tamper be?

Hi! How tight should a tamper be? I just got the 57mm Ascaso basket, which is actually 57.3mm, and the site where I bought it from recommended a 57MM DVG one (apparently it's made in Italy, but it's the first time I've heard of them - not that I'm that knowledgeable). Measured this DVG tamper with my calipers and it's actually 56.6mm, therefore 0.6mm smaller than the precision basket. I can't use my Lelit tamper with Ascaso because it's 57.35mm and, although it fits, it kind of scratches the walls of the basket. This DVG one seems to be a tad loose, I was expecting a tamper with exactly 57mm diameter. Waiting until Monday for a reply from customer service, but meanwhile I thought of asking you guys if I should be that picky?

People are also recommending Motta tampers, 57mm. Does anyone have calipers to confirm the exact diameter for Motta?