Can players choose specific points in space, down to the inch, to cast a spell so as to avoid hitting a prone character?


Say there is a character that is prone, such as if they were unconscious, and they are surrounded on all 8 square grids (assuming that a grid is being used) by other creatures. Can a player cast a spell that has a sphere effect such as fireball or shatter such that only the 8 creatures surrounding the one that is prone be hit?

Would this potentially have any adverse effects with potentially breaking or having any unintended consequences for any other spells/effects down the line if this were allowed?

Obviously when it comes to casting some spells, the caster has the option to "choose a point in space", but when playing with the understanding of a grid system that works in chunks of a given dimension does is it feasible to have spells cast in such a way so that a body lying prone won’t be affected by a spell cast just overhead?