You could change the width of each post to 25% in order to change the number of columns to four (the width is currently set to 50%):
@media only screen and (min-width: 1200px) {
.posts .hentry {
width: 25%;
}
}
You’ll notice, with the above custom CSS, that the default way the images are switched around doesn’t fit in well with four columns. You can fix this and get all of the images to display on the same side with the following:
@media only screen and (min-width: 1200px) {
.posts .hentry:nth-of-type(4n+3) .entry-media, .posts .hentry:nth-of-type(4n+4) .entry-media {
float: left;
}
.posts .hentry:nth-of-type(4n+3) .entry-inner, .posts .hentry:nth-of-type(4n+4) .entry-inner, .posts .hentry:nth-of-type(4n+3) .edit-link, .posts .hentry:nth-of-type(4n+4) .edit-link {
right: 0;
left: auto;
}
.posts .hentry:nth-of-type(4n+3).has-post-thumbnail .entry-inner:after, .posts .hentry:nth-of-type(4n+4).has-post-thumbnail .entry-inner:after, .posts .hentry:nth-of-type(4n+3).has-post-thumbnail .entry-inner:before, .posts .hentry:nth-of-type(4n+4).has-post-thumbnail .entry-inner:before {
right: auto;
margin-right: 0;
margin-left: -25px;
left: 0;
}
}
Let me know how you get on with the above.