The grid was designed specifically for 4 posts to be displayed. And the particular grid method isn’t automatic you would need to edit these two CSS rules in Customizer > Additional CSS:
@media (min-width: 900px) {
.wpsp-grid .wp-show-posts article:nth-child(3) {
grid-column: 5 / 7;
grid-row: 2 / 4;
}
}
change grid-column: 5 / 7;
to grid-column: 5 / 12;
@media (max-width: 899px) and (min-width: 600px) {
.wpsp-grid .wp-show-posts article:nth-child(3),
.wpsp-grid .wp-show-posts article:nth-child(4) {
grid-row: 3;
grid-column: span 2;
}
}
change grid-column: span 2;
to grid-column: span 4;
I would make sure to create a backup of the CSS, as i said it was designed for 4 images and was never tested for less 🙂