I think your assessment is pretty spot on regarding them not being able to expand. Just look at bthp pills when the tip is fully closed up and how they fail to expand even with the large tip cavity.
If I was @
dannyb I would section one of his 7mm Atips just to be sure. The 6.5 Atips might be different internally than the 7mm Atips.
@
sneeze the 147gr eld-m in my 6.5prc has been an absolute hammer on the deer I've shot recently (150m-500meters) (7 reds in last 2weeks) , a noticeable impact difference to the 143 eldx and 140gr gold dots. (I'm shooting bonded bulllets in the bush).