The perspective on structure visualizations looks larger at the back rather than larger at the front

This is usually due to having an inverted Z axis when calculating your frustum for the perspective matrix.

Either use an orthogonal projection, or invert the z before calculating your frustum.

Can you provide a screenshot of what you are seeing?

Actually, I've just looked at it again - it's rendered with an orthogonal projection matrix so when an altar structure is viewed e.g. side on, all the pillars front and back are the same size. It looks really odd when tilted, as the eye expects to see perspective (the back of the structure is narrower than the front) and doesn't get it.

Is there any way of changing to use a different projection matrix in the tome structure renders? I started looking through the code, but couldn't find anything obvious...

Something not leveraging vanilla.