ID-20LA Increase range, decrease interference between tags

We have an RFID tag reader system (ID-20LA) with 6 readers and ~9 inches apart. The readers must be that close because we are trying to track locomotor activity in a mouse home cage with 125 kHz glass capsules implanted in each mouse. We are having a double-edged issue: to minimize interference, we wrapped copper around the sensors. Although this solution mitigated the overlap of sensors, there was a simultaneous decrease in the reader range. How could we find a happy medium here?

Thanks!

Thinner copper wrap? Or maybe another material that has less RF blocking than copper?

Is enlarging the cage area an option? (so they’d be farther apart, on average?)

Enlarging the cage isn’t ideal, but certainly a possible route if all possible solutions are exhausted. Would aluminum wrap be a viable option?

Aside from interference problems, are there any tricks to increase range of the sensors?

Thanks for your help