Generally speaking (ie not talking specifically about stealth), you need to be more precise placing cards compared to omnis.
For best results, try to imitate one of the standardized configurations (DIN, ORTF etc), or just point them towards the stacks.
Also, using cards, they don't benefit as much from your head (or any other opaque body) being in between the mics, as a binaural set would do.
If they just stick out perpendicular on the sides, the pickup pattern will emphasize crowd chatter instead of music... But I guess you already know that.