In RP002-1.05 page 36 (line 666) of the LoRA regional parameters document it is stated that 16dB is maximum (and default) in the EU region.
the line of file eu868.go
EU868_DEFAULT_TX_POWER_DBM = 20
should read
EU868_DEFAULT_TX_POWER_DBM = 16 // page 36 RP002-1.0.5, 16 is the max

The value of 16 has been tested in the Netherlands (KPN network) for quite a while now.

I'm happy to submit a pull-request for this.