Baroque artists painted so that the pictures pops into focus when viewed from the distance of approximately 3 times the distance of the widest dimension. So this one is meant to be viewed from approximately 30 feet away. At this distance the viewer can see the whole painting without having to scan the eyes over different parts of the painting.
St Francis of Assisi: Illuminations by Matthew Paris
I wonder at the control that the 13th century artist had when working on such a small scale. He must have had exceptional eyesight to work without the aid of optical devices and modern lighting systems. I speak as one who at 61 years old, would struggle to match it with something twice the size even with the best reading and magnifying glasses and electric spot lamps!