All the implants are passive and are reliant on the power they can harvest to do what they do.
So a phone doesn’t generally get as good range as a desktop reader a desk top readers range isn’t as good as a parking garage reader.
Rosco uses a few high power readers, so he would be the best to answer the max range he has achieved.
You could probably get an idea from these ones that he used an xSeries implant
He also has one in his office chair (using FlexEM) and couch
This other thread of his also has some info
Need to? No
If you did, the reader may change its output power when communicating with a chipped implant (xEM or xNT) so you might get more blink for your buck!
There is a lot of anecdotal evidence that LF has better range (Physics also backs this up)
extreme example
Elephants communicating through the ground over long distances using very low frequency.
Roughly twice the distance as through the Air.
Something more relatable
WiFi range
2.4GHz better range than 5GHz (Data transmission performance is the inverse)