Hi again Jangeo,
I heard from St Lukes! There is indeed a large flat memorial stone for some Robinson relatives (which might include an ancestor or two). The transcription of it isn't complete, so next week the church will have their Verger cut the grass and uncover the Robinson stone. It's located three rows away from the main nave window (Plot 8, Grave 49). They are also willing to take a picture for me.