iPhone 16 battery

So I’m following the 30/80 % charging rule because apparently it’s better for the battery life and also because I don’t consume more than 50% in a day. So basically I’m charging the phone in the 30 min. I take in the morning to get ready to go to work. The phone is of course brand new and battery life still 100%. But I’ve noticed that sometimes the percentage goes from 80 to 75 in a couple of hours without using the phone while other times I find it at 79% after the morning shift (4 hours). Other times I play a game like sly the spire for an hour and it consume like 5%, while it can happens (like right now and it’s the reason I’m making this post) that I read a bit of news or social media for half hour and it consume 15% of battery. I know that different activities leads to different battery consumption, that’s not my point, what I mean is that sometimes I’ve the feeling that charging the phone to 80% in 30 minutes doesn’t always give the same amount of charge.
Has someone here experienced the same problem? Is still ok to charge the phone like I’m doing or should I just give a full charge every other day? I’m just looking for the best way to make the battery life last at 100% as much as possible