Here's the diagram I used on March 28. The bearing of the flat slanted edge of the boulder(red) is 318 degrees, so the triangle of light extends furthest to the right on summer solstice. There seem to be some slanting lines on the surface of the wall that the triangle of light fills up. This is more obvious at 7:37 and 7:49. There also seems to be a prominent vertical mark on the wall, to the left in the photos. It will be interesting to see how this structure looks at equinox and winter solstice.
The changing light did reveal three strange dimples on the cave wall, below the projecting stone, which is barely visible. This was taken at 7:58. Whether natural feature, symbol, or incidental product of Indian stonework, these were plainly visible and quite striking.