It's a ratio thing. I measure how I draw the head based on the eyes, and how I draw the body with heads as a measurement. You can do something like that too! If it helps to make the canvas too big so you can measure a ratio, then that's a great idea to keep it consistent. For your heads, since the eyes are so big, you may want to do measurements instead.
Idk if that's weird or not TwT
Maybe next time I'll try to use guidelines
Aaandd ofc give more space between the eyes if it's more fitting that way