HV Charge is least efficient mode
The manual says HV Mode and HV Charge are best used at highway speeds. As you noticed, the car will charge while idling, but not very quickly. My gas mileage in HV Charge mode on the highway has been about 28 mpg. The best mileage on highway has been about 70 mpg running in EV mode from full charge to less than half charge then switching to HV mode (which will work to preserve the remaining charge, sort of). Starting with a full charge and running in HV mode as soon as I get on the highway, for the duration of about a 160-mile trip, I got about 40-45 mpg. For your daily commute, maybe just run in default mode and let the car switch to the gas engine when the battery gets low. I like the suggestion of using max regen in Sports mode to extend the EV range and plan to try that myself. On recent long highway trips, mpg in Sports mode was about the same as HV mode alone. My rough calculations show that HV Charge mode is about 2x the cost of plugging-in at home. I still use it sometimes just because I want some use of EV mode at my end destination or just to run the ICE a little.