^^ Exactly. The "biggest" that Oberth in ST VII could possibly be would be attached to the saucer of the USS Farragut
. The further it gets away / the closer it gets to the "camera" it proportionately shrinks in size in relation to this Nebula.
I'm sure that what we see at the end of ST VII has an easy explanation. IIRC the VFX shots were done by ILM and to composite the VFX single elements in correct scale they relied on the Nilo Rodis (ILM) size comparison chart he made for ST III which never intended the Grissom
to exceed 120 meters.
I think that's especially obvious when we look at the NCC registry on the engineering hull / pod of Grissom
which compared to other outer hull markings would be unusually big for a Starfleet vessel exceeding 120 meters.
Agreed, the docking port decal of the Pegasus
suggests a bigger ship, but early on in this thread I recommended we look at this possibility.