The grid is too small, people with small phones, large thumbs, and certain disabilities such as myself often end up having gems go different directions than we intend because of how frustratingly small it all is. There is nothing more frustrating than setting up a stun over two turns to have a gem go the wrong direction and then lock you out of the combo and effectively waste your turn.
There is PLENTY of dead space to expand the puzzle space, or you could ad a toggle option to make the grid full screen and minimize the 3d models.