Distance from pistol grip to vertical foregrip

I'm an artist designing a very large (fantasy/scifi) weapon for a character who is 6'2". I was easily able to look up what a good length of pull for that height is (I'm using 14"), but everything about where to place the foregrip says "where your hand goes"! That's great practical advice but not helpful to my circumstance.

Well, I'm significantly shorter than 6'2", and I don't have a 6'2" friend who could try to model this for me, lol.

Can someone around that height please tell me what they have (or would have) for that distance?

As the gun type may affect that, for context this gun is basically supposed to be a huge vehicle or tripod mounted gatling gun modified for a very strong person to wield unsupported. Because of how weird that is, I'm basing a lot of details loosely on AR-15 and similarly shaped firearms.