My theory differs from the popular take. If you look closely, the nipple itself is a hex head that matches nicely the hex head at the tip of the JPS bracket? that is coming from under the foot shroud. I should add that that hex head nipple's location lines up nicely with the bracket too.
I think they placed that bracket right onto (and slightly in) the below JPS piece. The dome? - hot or thick glue that found it's equilibrium drying viscosity as the "dome" you see.
That's how I've pieced mine together. I'll try to sculpt some apoxie later to make the dome.