Thanks for the reply.
Was it the case that enemies would pass through the shield sprite and yet you would take no damage? If so, that was intended. Your ships hitbox should be slightly smaller than the actual ship sprite. This is to basically make dodging enemies feel more streamlined.
I'll think about ways I can make this more clear, as your assumption that your shield would itself register collision is very intuitive.
Thank you again for the in-depth feedback.