Thanks to all for the suggestions.

Hmmm ... as dcb says, I am not sure if it is a good idea to put all weak cells in the same group. For simplicity, assume discharge not more than 1C, and the configuration is 10s5p. Assume 45 of the cells are 3000 mAh to cutoff and 5 of the cells are 2500 mAh to cutoff (the weak cells).

If the 5 weaks are grouped together, then cutoff for the group happens at 2500 mAh per cell (i.e. when 5*2.5A has been drained from the weak group). This means the other 9 groups each has 5 * 0.5 = 2.5Ah of unused capacity. So total dead capacity = 2.5 * 9/10 = 2.25Ah.

On the other hand, distribute the 5 weak cells, one per group. So cutoff will happen at (4*3000+2500)/5 = 2900 mAh. There will be 5 groups each with 100 mAh of dead capacity per cell. So total dead capacity = 5 * 0.1 * 5/10 = 0.25Ah. Which is much less.

When a weak cell is grouped in parallel with four strong cells, I don't think it is the case that cutoff will happen at 5 * 2500 mAh. Rather, cutoff will happen at 4*3000 + 2500. Being in parallel, the stronger cells will supply more current proportionally while the weaker supplies less, and thus the weaker cell cannot get over-discharged. Their voltage will always remain equal. If the current is cut, and the five cells separated, the five in parallel will have same voltage. One weak cell cannot disproportionally reduce the voltage when in parallel. In series, it will disproportionally reduce the voltage, due to the "first past the post" cutoff.