I assume you meant to write "6.6 kW chargepoint delivers 6.1 kW" because I'm not aware of any EVSE that limits the energy delivered to an amount like 6.6 kWh.
The power of EVSE (kW) is determined by the voltage and amperage. If either is lower than expected, the power would be lower than expected. The voltage is outside the control of an EV's charger and depends on the load on the charging circuit or in the local area and the electrical resistance of the power wires.
An EV's charger does control the current by telling the EVSE what current to deliver. As a battery pack nears a full charge, the charger will tell the EVSE to reduce the current and thus the charging power.
So it's normal for an EVSE to deliver less than its rated power as charging approaches full, if the supply voltage is lower than the rated voltage (likely 208 V for a 6.6 kW EVSE), or if the electrical resistance of the power wires results in a voltage drop when delivering the relatively high charging current (e.g., 30 A).
2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE