The tabs carry the current for only one cell. The bus carries current for the whole group, so naturally needs to be bigger. Me? I would use .2mm thick nickel as wide as you can get your hands on. Series connections with some husky braid or better, and arranged so that current travel through nickel is minimized. 225 amps continuous for the 5p is no joke, if you actually intend to pull that much from the battery. What’s it pushing?