Once again I stick to flat betting and a grid. Line 1-6: 1-6. Line 2: 7-12. Etc.
When only four numbers out of six have come, there are 15 possible combinations. Probably the four numbers do not form two groups.  Only three combinations form two groups. For example 1&2 and 4&5. 1&2 and 5&6. 2&3 and 5&6. Nevertheless I  bet that four numbers form two such groups (flat betting). 
In the grid we have six horizontal and six vertical group. 3/15 X 12 = 2,4.  In average we should expect  to see the pattern 2,4 times. 2,4 hits
I end the session at the latest  when only seven numbers have not come.