Does the picture
here ** answer your question OP?
Also -- and someone correct me if I'm wrong -- AH only confirms connection integrity and data origin of your packets,
but NOT encryption. ESP does all of what AH does AND encryption. IIRC this has nothing to do with IPv6 itself but
is a "legacy" item from IPSec's early days.
** original source --
here, in figure 2 "IPv6 IPsec Packet Format"
Regards