Observation is having properties. The properties of observation related to the object are most important.
"At the same distance the object looks the same" we can say the easy way.
For light we measure frequency and amplitude when the photon arrives here. The impact of gravity regards the gravity of the entire object between source and observer. This assumption derives from the event horizon of black holes.
The calculated impact then resumes as difference in mass of the black hole and it's assigned observation sphere.