Toilet rocks on dry fit.

I just put new tile in the bathroom. Coincidentally the design pattern that I chose allows the toilet to sit all on a single 12 x 24 tile. Not sure if this a good or bad thing, but seemed convenient.

Upon dry fit just now, I was testing for any movement. Putting weight on the front of the toilet causes a slight rock and a thud when it moves.

Obviously I haven’t grouted the tile yet. When I grout, I plan to also grout around the base of the toilet, leaving room at the back for leak detection.

Is this normal? Should I need to shim a toilet sitting on a single tile. Do I need a shim, or should the grout be sufficient to hold it in place? Should I return the toilet?