The Zoomin page view gives all of the Story River tiddlers position: absolute;
which takes them out of the normal flow. That’s why the Story River doesn’t wrap around them anymore.
To add some extra space below the tiddler, you can try adding an :after
CSS element to the tc-tiddler-frame
. Here’s a starting point, to see if you can get the effect you want…
.tc-tiddler-frame::after {
content:" ";
position: relative;
height: 5em;
bottom: -8em;
margin-top: -6em;
display: block;
width: 100%;
background-color: #ff00ff26;
}
This feels fairly hack-ish, but seems to get the job done.

Adjust the following values:
height: 5em;
bottom: -8em;
margin-top: -6em;
Once you figure out a combination for the desired spacing, you can remove the background-color to just have empty space.