In general a minimum bend relief is equal to the material thickness plus the inside bend radius.
Sheet metal corner relief size.
For a 3 width ratio when the part is 1 mm in thickness the width of the slot will be 3 mm.
If you use the close 2 bend corner tool you can take the two corner types shown above and they will look like the closed corner shown below with the flat pattern to the right.
When considering sheet metal thickness a single sheet with punches holes is a good rule of thumb.
This option is straight forward.
The way this one works is that you select the tool first found on the home tab sheet metal group.
When sheet metal makes a transition from a bend to a flat surface or to another bend it tends to rip and tear.