Just looked them up..........They are not open today their phone number is there though, they state they are penmaking experts ,will give advice. Why not go there all their examples have that same dip in the centre, they designed this from the Euro kit they say.
Was there a set of instructions? Does this show that funny join in the centre. Is there a removeable centreband if not take the pen apart and return to suit the design you prefer. It would have been obvious as you turned as well the bush being so high compared to the metalwork..
THis is why its a plan to check sizes with a caliper. If your wife is happy with the design you made make a gift of the pen to her.
All the best ............Peter.