Classic Solid Tiny Thong

The sizing of these is so strange. For reference, I am 5' 7" 140 lbs, 36/25/36, I bought a s/m, and it fit weird, so I got a m/l, and neither one works! First of all, if you wear it like a normal thong, on top of your butt, at your actual waist, it either digs in to the point of being unsightly, or gaps weird in the front. The only way to make it fit even close to okay is to wear it at a super low angle, the way the model in the picture is wearing it. On me, the s/m still digs in to my hips and buttcheek, whereas the m/l just falls off with the slightest touch. I bought this with the intention of creating a smooth line across my hips and rear, so the idea that I should cut literally straight across it in the middle of my cheek is ridiculous. Come back to me when you make a thong that actually is invisible (i. e. doesn't create vpl across my rear or my stomach).