Most folks know bookshelves pull off the "disappearing act" much easier than floor standers. When they don't it typically means there's something about the room setup (reflections and room modes) that's ruining the illusion.
Changing out any upstream gear (cables included) often requires a fresh examination of speaker placement. I just changed DAC's and that had me moving my speakers 5 inches closer to the rear wall and 6 inches closer to the side walls, with a tad less toe in.
Even with great room setup poor recordings will almost always tell you exactly where your speakers are. It's just something we sentimental people occasionally have to put up with.
Listener position is also a factor, which some forum members have already commented on. I have two positions that I like to bounce back and forth between. The first being the equilateral triangle, which gives me a smoother, more refined presentation. The second being the "89% setup" aka. nearfield. The "89% setup" gives me a more immersive and exciting experience. In my rig my speakers do a great job of disappearing at both listener positions, which should tell you listener position isn't the most critical factor, but nevertheless shouldn't be ignored.
So it's really an alchemy of these five factors (gear/recording quality/room treatment/listening position/speaker placement) that determine whether or not your speakers "disappear", and the only way to achieve this is to experiment. Rules of thumb are great, just don't fall into the trap of any one dogma. The best in the business have spent decades crafting their setup skills. The whole process of exploring what works and what doesn't isn't just about finding the sweet spot (for you), it helps train your ears.
Then there's the whole realm of psychoacoustics to explore, but that's another topic and deserves a good bottle of wine to go with it ; )
Happy listening!