1.3 groups work, just not as well as the 1.3.

With the 1.2 groups you will have:

1.) A more consistent baby dropping schedule every three weeks
2.) Faster growing, healthier kids.
3.) Less food waste per produced kid.
4.) Highest number of kids per breeder female per month.

The way you changed the groups is fine but you still want to hold back the first babies they produce and completely replace each group as soon as possible. They will never get along as good or produce as good as a group that hasn't been tampered with since they started producing.