"Inversion!" Max exclaimed as he struck out a fist.
Sandman didn't know why but she felt extremely threatened by the approaching fist. There was nothing special about it on the surface but for some reason, she felt like something bad would happen if that fist touched her.
"Impossible, I'm feeling threatened by a human child?... He is nothing like those stupid Sages from back then so what is this?" Sandman thought. But even with her hubris, she wasn't willing to take any chances. Not in the slightest.
Unfortunately, she could not afford to step out of the automatic defense she set as it would take time to set it up again, time that she could not afford.
Of course, she couldn't just wait for Max's attack to reach thus she reinforced sand into the area Max approached from, leaving the other areas slightly lacking.
A necessary sacrifice to ensure her survival. Sandman assured herself and prepared to kill all three Max's the moment the one in front got stuck in her defense.