Your salesman most likely doesn't own a Clarity and has minimal experience. If you download and read the manual there's a lot of info to digest but here is the short version.
Around town on your day trips E/V is very economical. If you accelerate too hard, it may run the gas engine to add power to the electric motor.
When going onto the HWY, EV by itself depletes the battery very rapidly. Use H/V to maintain the charge you have.
If you're on the HWY with a minimal charge, you can use H/V Charge to bring it up to about 60% after several miles of driving. Then it will drop back to just H/V. But you'll maintain the charge for when you're back into rural or city driving. But you have to be patient, it may take more than 20 miles of steady speed to start raising the bar. And like any car, the economy drops off very fast over 70mph. Also keep your tires at 36psi checked while they are cold.
Hope that helps.
We purchased our new base model Clarity plug in Hybrid June 2018. We told the salesman we drive to FL for the winter, a total of 1,400 miles and we needed a fuel efficient vehicle to do this. He told us to start on electric and when depleted switch to HV charge to recharge the battery. I have experiments and found at no speed on HV charge does it recharge the battery at all. Don't expect full charge but I am talking not even one bar of juice. No one at dealership knows much about the operation of this car beyond plug it in get 47 miles then it goes to gas. Can anyone help since we are leaving shortly. I hope we were not sold a bill of goods.