In the blockchain limit, $x \to 0$, the cohort time is approximately $$ T(x) = \frac{1}{\lambda x} + a + \mathcal{O}(x) $$ which allows us to see that the quantity $a$ is the increase in effective block time due to network latency effects. This is to say that the actual cohort time is slightly longer than expected from the hashrate.

The right side of the above graph can be understood intuitively as well: for large targets (low difficulty) we are producing beads so fast that there is nearly always one in flight. The only way a cohort can form is when there is accidentally a quiescent period where no miner produces a bead. The probability of that happening is exponentially suppressed.

The use of a braid allows for a zero parameter retarget algorithm which instead of targeting a fixed block time, targets the fastest possible block time. Evaluating the above for the Bitcoin network, which has had an orphan rate of 1.16 orphans/day on average over the last 2 years with a block time of $600$s, we find that $a=4.79$s and the cohort time at the minimum is $11.64$s.

It should be noted that even if a coin desires to have a fixed-block time for other reasons, it is still desirable to allow the merging of blocks, whether they would be orphans, or are due to a network split. The above analysis still applies to such a scenario. The extra blocks are called "orphans" or "uncles" in those scenarios.