Painting over visible corner beads

Hi all - I am looking for some painting advice. I've just finished a second mist coat over the plaster and have noticed that the imprint of some of the metal corner beading shows through. I did a quick look on YT and found a recommendation to use the zinnser stain cover. I had some laying around so painted a couple of inches either side of the corner covering the bead. This does appear to have hidden the metal but presents a new issue, the zinnser paint now stands out instead. I've tried rolling two neat coats of emulsion over the top of the zinnser but it still clearly visible underneath. 

Is there a right way to do this? I did try a little light sanding but this hasn't really helped either. Rolling the zinner on doesn't seem appropriate for this type of paint. 

Thanks, Paul