Short answer: The button auto generate the minimum possible group size.
Long answer:
Looks at the right-most two digits, 00, 04, 08, 0C, 10. For example, you searching XX;YY, which are two adjacent DWORD, the group size will be 5, which is counted by 00, 01, 02, 03, 04 (5 addresses apart). This is because one DWORD hold up space of 4. Meaning 0D eating up address 00, 01, 02, 03. By toggling the byte, you can see more addresses hiding between 00 and 04.
So for example you are searching XX;YY;ZZ, the group size will be 9, which follow the formula 4n - 3, where n means how many values are there.
XX;YY n =2
XX;YY;ZZ n=3
XX;YY;ZZ;aa n =4 and so on...
Then the button generate the smallest possible group size depends on how many values you are trying to find.