High PER at 2Mbps

Hi,

Scenario:

Two nRF52832DK boards on a table, approx 20 cm from each other, +4dBm output power.

Payload length is ~60bytes.

Running at 1Mbps gives me less than 0.1% PER, running at 2Mbps gives about 25% PER. (everything else kept identical)

Is this expected, or is there something at play here?