The JIRA details shown in current JIRA Issue component only takes up 1/3 of the section in which it is placed.
There is a css tag being placed on the component 'slds-medium-size--1-of-3' that is causing this.
If this tag was removed, or if we could add our own tags, or be given access to customize the component, the display issue would be fixed.
I've attached screenshots of what it currently looks like, as well as what it would look like if that css tag were to be removed.
This idea has been addressed with the release of the "Beta Lightning Web Component", howeer the expereience is different, you can expand each card in a side bar to view details in a more intuitive manner.
Aidin- Product Manager