IHT, NIC - (paid by/suffered by)

I am getting it wrong everytime question pops up regarding this. When taxpayer dies, IHT on lifetime transfers is always paid by the person or trust who has received it. IHT on death estate is BORNE by the residual legatee which means he gets the leftover residue estate after deduction of the IHT, but that IHT is PAID by the Executors/personal representatives. In case of NIC, if there is a self employed person(X) , who has an employee (Y) working under him, the class 1 primary nic is paid by X but suffered by Y , however all other-class 1 secondary,class2 and class 4 are both paid and suffered by X. Please correct me if I am wrong and suggest some additions or any other scenario possible here that could create confusion.