The above post is one approach. I ended up using a different approach.
I find my Avanti Quattros to be particularly tiring for sustained flutter kicks in current. I tried to 'learn the right way' to use them for a few weeks and experimented with different kicking styles. Then I realized that everyone is different, and there's no single 'perfect' way to fin. So I said 'screw it' and tried some different fins. In the end, I found something that fits my style, needs, wants and strengths.
The reason for sore calves could be from finning technique. It could also be a side effect of the way a person walks, what they do for a living, how they exercise, what they eat, or how they were made. It's not wrong to address all of those things so that you don't get sore legs when you dive. It's also not wrong to try different fins so you can enjoy diving more without changing anything else.