The SHGC is depending on many factors and is mainly influenced by the build up of the entire stack of products: is there a low-E coating applied, is it double or triple glazing, what is the thickness of the glass, etcetera. This in turn is depending on the climate zone and other choices which you make during design of the façade and the rest of the building.
However, a part of the infrared light is reflected by our smart glass. In the visible spectrum, as we absorb the light, physics tell us that the substrate becomes warmer. This heat is dissipated from the window by radiation (both inwards and outwards), convection and conduction. In its fully tinted status, the glass heats up the most. The energy which would otherwise heat your body or the inside of the building is absorbed. As there is radiation and convection to the outside, there is less heat gain than through transparent glass. The exact amount however is design dependent.