Cycles are also partial. So going to 40, then back to 80% is about a half cycle (40% for sure). Do that two or three times and you have more than a cycle.
Don't sweat 18 cycles. If you go to 100%, then down to 50% for a half cycle every day, that will be about 185 cycles in a year. Cycles don't start to degrade battery performance until you get to about 1000, so that would be 5-6 years of use that way.
What to avoid as much as you can are deep discharges. Below 40% is really hard on the chemistry of the battery. So stay in the 50-95% range and you should be good to go. In fact on that iPhone Apple has smart charging, where over time the charging circuit "learns" your pattern of use and charging and will stop charging to hold the battery below 100% until just before it anticipates you wanting it, and then sprints to the 100% level for you. So leave it on charge overnight and in the morning it will show 100%, but won't have been there very long, which is a good thing.
Bottom line, don't sweat the cycles, don't discharge deeply and just enjoy the iPhone.
