Ответ ашала был довольно интересен, но что ему мешало и мешает повырезать все эти древние секс сцены?
rough behind is an old animation from mini lovers, it has a small offset which makes it impossible to line up with the player unless collisions are off. It should line up fine for npcs using it together, just not when the player is involved. This animation is pretty much the sole reason the Toggle Collisions options exists in the MCM menu for sexlab, it will toggle off collisions for sex and then toggle it back on afterwards, it can cause oddities if your in a busy area or have multiple pairs going on at once though.
If you don't want to turn that on for all animations, than your only option to align it for the player is to open console, enter tcl, then press the realign actors hotkey/restore offsets hotkey.