i'm running up against what appears to be a limitation on the hardware side, that of the LF transmission power. small tags often don't respond to transmissions as they cannot receive it. larger card size tags work fine.
i've snooped the transmission with another pm3 and the transmission power of the pm3 is significantly lower than snoops of valid readers, especially when it comes to maintaining long high peaks. (low peaks don't seem to be a problem...)
(this affects lf simulations, hitag, em4x05, and other lf tags that require two way comms.)
is there a way to add a component to help this issue or some software work-around someone has done?
(btw, i'm running standard (old) pm3 stock boards mainly from proxmark3.com)
 additional info:
place a em4x05 card on the antenna (40v) and issue a new lf em 4x05info cmd and it works fine.
pull that card a cm away and it fails to receive the command to get into the command mode of the chip.
keyfobs never are able to go into command mode despite verifying the command sent matches that of another reader that is able to get the fob in command mode.