I can share you the information which I got from them before. TL-ER5120 - 512 TL-ER6020 - 128 TL-ER6120 - 512 TL-R480T+ - 128 TL-R470T+ - 64 Hope it can help you. But this means the Entries number...

I think this SNR is just the status of your network environment. The cables, devices and modem as well all affect it . I am sorry that you can not adjust it.

In the web interface. you can go to System tools-->system log . you will see what happened.