The LASA Laboratory (INFN, Milan) is working in the High Luminosity LHC program for developing, in collaboration with CERN, 6 different types of High Order corrector magnets. In this framework, in parallel with a conventional design of superferric magnets with LTS conductor, the LASA Lab. is focusing on the research of novel superconducting materials which may have application in particle accelerator magnets. To this purpose LASA Lab. is developing a new type of superferric magnet suitable to arbitrary multipole order, called Round Coil Superferric Magnets (RCSM). The iron yoke shaped with arbitrary poles is able to create the desired harmonic component using only one single round coil with a large bending radius which is suitable for very strain-sensitive superconductors. The electromagnetic design of a sextupole configuration of the magnet and the production of the first superconducting MgB$_2$ round coil prototype have been already presented. In this paper, we expose the optimization of the iron yoke and polar expansions assembly of the first magnet. The results of the whole magnet powering test are described in detail and the analysis of the magnetic performances are compared with those of classical superferric correctors.