OAG for a Askar 71f, 48mm or 54mm

Hi, some newbie advice about which size OAG to buy for my Askar 71 please.

My 71f arrived today along with the Nikon adapter and a filter draw. I’d like to buy a OAG for the guide camera, but an uncertain whether to get the 48 or 54mm version. The screw thread for the adapter is 48, and there’s a 54/48 reducer. LogicalLy to me it seems sensible to get the 54mm version so the OAG will sit in the wider section of the scope and will have less impact on the APC sensor in the camera.

Os my thinking correct?

Cheers