I was able to compile Domoticz under a Ubuntu Hyper-V VM, so I can try to understand the code, and you are right, the "whLifetime" into net-consumption decrease when exporting to the grid.
So, I fear, that we can't do nothing on Domoticz side finally, and in final, it's good to have a Linky plugin working to know exactly the "net-consumption"
So in fact, it's an Enphase design, now I don't know if it does that before V7 firmware, I'm pretty sure native doesn't decrease the counter on V5 firmware, and I was also using Node-RED to MQTT previously and with this URL to getting information to parse to Domoticz :
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With this streamer URL, it's nice to get data quickly without problem and it's running fine like the data arrives all second by itself, bu I think it's only an a metered S device !