it's been a long time since I had any, but I'm 90% sure 5th avenue wheels are the same way, they have the cavity there to fit the heads of the little bolts used to hold on the hubcap retainers...
if it's flexing, then maybe the wheel vintiques wheels use a thinner gage steel for the center part of the rim? you could measure the depth of that channel (guessing somewhere around 3/16"?) and get some small OD washers to put on the stud before putting the wheel on to take up the gap....