A Speedo style swim brief that fits around the waist and completely covers the ass crack should fit firmly but an Arena style swim brief that rides on the hips and begins to show some ass crack needs to fit more tightly, compressing everything into the space available and gripping the body. Once you minimise a suit and have to add a pouch at the front it doesn't need to be so tight.

How do you wear your suits?
 

I wear speedo racer style briefs that cover me well and fit nicely. Those water polo swim briefs do fit a little tighter, but do keep my front snug and secure with the rear fitting almost like a semi thong fitting in the rear. They do expose the lower rear cheeks and really fit and feel great, yet not too. tight

For a tighter fit, look for "flat front" suits that don't have a front pouch but still have full rear coverage. My cyclist buns are firm but I like the snug feel of my flat front Mategear suits.

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I love wearing my speedos the tighter the better especially if they aren't so stretchful. The feeling of having my equipment stay in place while squashed in that tiny, snug suit, all my fav suits are downsized on purpose 😆

Small suits
 

The tightness and brevity of the suit is all important for me . I love relatively small front and side profile and about 3/4 coverage for a U.K. pool . Abroad I will go down to string sides virtually . Half backs and tee backs are fine here too . I prefer a nice feeling of support so not so keen on string rear . I also prefer the flash of colour at the rear of a thong rather than a string .

For me, the tight fitting, low rise Neptune Scepter suits hog my body and give nice presentation without offending people around me. The small sides are a also important.

The Mate material is stretchy so this is more comfortable than a larger AQUX suit My photo https://photos.app.goo.gl/6V58chFsePp5nTzdA