Those numbers of 1470x956 are “points” or “looks like” values, not the size of the frame buffer. The frame buffer for “looks like 1470x956” is exactly 2x that, or 2940x1912. On a 2560x1664 display, that’s a 1.148x scale factor. Again, nowhere near 2x, even on the “more space” setting.
If you’re counting by the framebuffer than the only 2x is the hidpi-forced-into-lowdown like the link suggest. The ratios I’m referring to is the UI scaling against the physical display pixel dimensions.
Apple basically settles into 220 dpi physical displays (250 moc MacBook Pro), rendering UI at a 2x scale as a default, except for MacBook Airs.
When you set it to "more space" it becomes noticeably slower, but not blurry.