How can i move a part with bodyvelocity based on its size?

local speed = 50 i made it so as long as you hold the button the size Augments and when you stop pressing the button the remote fires and the Body Velocity is made and the BodyVelocity is multiplied by the speed ,but i wanna make so the bigger the size the slower the speed gets , i have managed to do the inverse, but i have no idea how to do it any help please?

local speed = bullet.Size.Y*2

 local Woosh = Instance.new("BodyVelocity",bullet)

    Woosh.maxForce = Vector3.new(math.huge, math.huge, math.huge)

        Woosh.velocity = CFrame.new(plr.Character.UpperTorso.CFrame.p, Mouse.p).lookVector * speed