Anyone know how much fluid to run in Moroso Coolant tank for an NA?

OEM tank died and i replaced it with an overpriced but very pretty Moroso tank. It came with zero documentation and they have no instructions on the site for what level to fill the tank. Tank has no site glass, and it has a weird side fill spout not like oem tube. figured someone here had one and knows. I assume run a level over the side spout?

 

If the OE hose fails, you'll be sucking in air, so with the NB, Mazda moved the spout to the bottom of overflow, sounds like that's where moroso put it. Level isn't too important, just make sure it's not empty when cold.

 

Moroso finally answered the phone. for anyone else, they said fluid level above the brass fitting, level with the first hump.