How tax much depends a whole lot on your circumstances. Where is the money parked? Ar you gonna move it to low tax canton like SZ? Are you withdrawing while being a resident of CH or of your new country? In the latter case your new country may have dibs to tax you according to their laws too. Though you should probably be able to get the swiss taxes back in that case
That calculator is only for ordinary cases of a withdrawal by a CH resident, beware. So probably doesn't apply to OP. Non-CH-resident withdrawals have different rates, use this calculator from liberty it's spot on: https://www.liberty.ch/en/vested-ben...thholding-tax/
You are correct that for non-CH-resident it's the canton of BVG fund that matters. Park the money in SZ and withdraw after moving abroad, it tends to be the cheapest for that as far as swiss taxes go. Consider foreign taxes tho. And withdrawal fees, all schwyz funds charge 3-4 figures per withdrawal, whereas non-SZ funds usually don't charge anything for this and are usually very happy to release the money asap to avoid getting hit by negative interests