The 4-in-1 PTFE adapter should be connected before the buffer on both the H2D and X1 Carbon if you’re attempting to use them as an AMS. However, if the intention is to use them as an external spool, the adapter should be connected after the buffer. On the H2D, the bypass port must be used in that case — and the same applies to the AMS HT: the bypass port must be used, otherwise it won’t work properly.
Also, if you’re currently using only a single AMS, a 4-way buffer is required to ensure everything functions correctly.