Add some more putty from the bottom of the visor to below the chin. The layer mustn’t be too thick, though. Form a rough mask shape with your sculpting tool/fingers ( a triangular mask always looks good on these guys), then smooth it out with your sculpting tool. Now, ensure your sculpting tool is wet/lubircated, and, using the pointy end, gently press a couple of folds into the cloth mask you’ve just sculpted. If you want a straight edge, you can wait for the putty to cure, then use a knife to cut a nice, straight edge.
Et voila! One dynamic Junker Legionary. This pose would be ideal for the Desert Fox legion in particular, with their emphasis on speed.
Also, with only a small amount of work, you could convert this model into a thermite lancer, by replacing the sword with a spear-type weapon, or a suicide bomber, by leaving off all the weapons and the shield, and adding small rectangles of putty or plastic off-cuts to the torso area to represent the explosive charges.