 Complete-intersection candidate family

Two members of this uniform set family have at least $2(t+i)-(t+2i)=t$ common points in its distinguished prefix, so it is a t-intersecting family. Nonempty indices satisfy $0\le i\le r-t$. Consecutive-family size comparison reduces to the threshold $n_{i+1}=(r-t+1)(2+(t-1)/(i+1))$: gain sets contain both newly introduced coordinates and $t+i-1$ earlier points; loss sets contain neither and $t+i$ earlier points. Counting these sets with binomial coefficients proves increase below, equality at and decrease above this threshold.