Well, cataclaw lost M3, flame engies and shock squad to a single mine field.
All mines are really potent.
Try sometimes placing a teller or minefield instead of getting LMG, grens don't really need these LMGs to beat cons.
S-mine fields come with obvious signs, cost twice as much and gives its victims the chance to halt if they stumble upon it. If a S-mine field wipes a squad it is usually due to incompetence on the Soviet side unless it is placed in a retreat path. Soviet mines are stealthy sons of guns that regularly wipe entire squads that step on them.