I believe that Six Senses is not fully intergarted into the IHG One Rewards programme, so earning and redeeming points are not available at all properties. The IHG One Rewrads T&Cs state (my emboldening):
Members may not be able to redeem Points for Reward Nights at InterContinental Residences, IHG Army Hotels, and Six Senses Hotels Resorts Spas.
Not sure how you chose the properties you checked, but redemptions are available at quite a few Six Senses properties, some at mouth wateringly high rates!