The Felt F series and Altamira are not the same frame
The F series uses BB30, the Altamira uses BB86
The top tubes have a different shape, the Fuji's narrows more towards the seattube
The geometries are WAY different; Felt size 56 is stack=548, reach=397 / Fuji size 55, stack=579, reach = 388
So for an equivalent reach, the Felt has +3cm less stack.