I think said another way, if the heat is too high, a higher proportion of liquid is boiling off faster than is cooking, i.e., penetrating and hydrating the rice. So you have to add more liquid, and it might take longer to get the rice done.
Older rice, with less moisture in it, will absorb more liquid than fresh rice, too.
I make quite a bit of risotto, and I think you can't slavishly adhere to recipes for it, especially in terms of liquid and timing. It's done when it's done, when the mouthfeel is right, and if that takes more liquid, so be it. sometimes I even add water at the end if I've run out of broth.
I also hardly ever heat the broth that I add, and I can't say I notice any difference. However, my risotto usually takes longer than most recipes say, so maybe that is a factor.