When someone says "voltage
and wattage" - as though they might require being adjusted in concert with one another - I have to assume they don't have a good understanding of VV-VW APVs. So... in that context, you might want to read this.
Taking The Mystery Out Of Variable Wattage
Also, as you don't indicate what APV you have, and what that APVs amp/watt/volt limits are... there is no complete answer. If for example you have a Innokin
MVP2, with a 3 amp/11 watt or 6 volt upper limit, then I'd suggest around 8.0-9.5 watts
or 4.5-5.5 volts. Fine tune as needed for the juice.