Thanks for the example justjennifer! There are a couple of differences between the images in the sample gallery you've made and the images in the gallery moody3576 is making.
1) All of the images in moody3576's gallery are fairly small - 300 x 168 pixels. This doesn't leave a lot of wiggle room for the gallery to scale your images to fit. In contrast, many of justjennifers images are over 1200x1000 pixels.
2) Along the same vein, the ratio of width:height in justjennifer's images range from 1.2 to 1.33. All of the images in moody3576's gallery have a ratio around 1.75. This is a drastic difference for the tiled gallery where that ratio is used to place images next to each other at varying sizes.
3) There's a lot of variation in the size of the images in justjennifer's gallery, the largest being 4000x3000 and the smallest one I found around 600x500 pixels. In moody3576's gallery, other than the very last image, they're all the same exact size (plus or minus a pixel).
Between these factors, there aren't any images in moody3576's gallery that can take up vertical space while allowing for images to be stacked next to them, for example this section from my test gallery (I didn't want to screenshot your gallery, justjennifer, since it's published privately):
And with only seven images, there isn't a lot of manipulation the gallery can do.
To reiterate, your tiled gallery is working correctly moody3576. But your images don't allow for much manipulation.