Velocity stacks flimsy fit ?

[HWB]

Hey gents i fitted 50mm velocity stacks (genuine mikuni) on my flatslides 38, i notice the stacks dont go all the way in, seems like there is abou a 3mm gap before it completly sits in properly. Is it supposed to be this way or whats going on ? 

[dago]

Just checked mine, 50mm on 38s are the same, slight gap, think it might be because there's a slight radius on the back of the flange, looks like they're spun so part of the manufacturing process