Bad coverage under side

Hi guys
As first lte sites that we have activated I have similar problems in all of them
Under site I am not getting good RSRP and thrp but when getting far little from the site the situation got changed by better quality and rsrp
Can you guys let me khow what can be the problem
The vendor is Ericsson and all my parameters are baseline for all sites
The RS 18.2 and the power is 40w .tilt can not be problem because by same tilt as BB I do not have problem as 3g

If you confirm that antenna setup and power configurations are correct for LTE and 3g, let me guess a little bit.

Since Tx power is 40w, (46dBm), and very strong under the site (3g), then for LTE, is may be signal in UE’s RX is too strong to fall in the AGC adjustment range and ADC saturate, then RS reception is not stable. Thus RSRP estimation is not correct and throughput is low. For 3g, I guess if it adopted WCDMA (spectrum spread) and with the specific UE Rx design, this problem may be a different story.

I suggest you use the test equipment to do drive test and check RS reception and BLER of the receiver, e.g, Keysight or Rohde&Schwarz.