Issue type with custom icons are showing bigger on some screens.
- This issue can be seen on Custom fields > Click on Configure for any field > Edit configuration > Choose applicable issue types.
- Depending on the issue types of a service desk project, the issue can also be view on Project settings > Request types.
- Backlog of a Classic Scrum project.
The icons show as a normal size.
Some system icons and also custom icons are bigger than the others.
To work around this you can try replicating this white margin in your custom icons
The only way to have the custom icons actually match with the default ones in the UI, it would be necessary to have white borders on them as well. You can use any image editing tool such as to add borders.