Subgroup Size on High-Mix Process

Good afternoon,

I would like to ask for opinions regarding subgroup size please, on a high mix process.

Generally at least 3 pieces of a lot of  regularly 30 pieces are measured (first, mid and last), the lot size may be bigger thus increasing the amount of pieces inspected too, the same part number won´t run again at least for another two weeks (except on high demand part numbers when sometimes is less).

For a CPK analysis, what would be the best approach for subgroup size on this scenario? should we consider one lot as a subgroup (s.g. size=3)? should the sample pieces be taken consecutive instead?

Thanks in advance for your help,

Israel