Yeah, previous iPhones were always suspect in their antenna placement and outside housing material choices.
My HTC is full-strength (3 bar display) when I hold it normally, or set it down; if I cup the entire top of the phone then it drops to 2 bars. It’s nearly instant (like 1-2 seconds) to respond. You can get the bars to dance back and forth by holding normally or cupping.
It’s really all about antenna placement and materials used; in my HTC, the antenna is at the top, on the back, and the rear housing is made from plastic (I believe HDPE). The material is transparent to EM fields (unlike metals), and the placement of the antenna is in a location that is VERY hard to naturally cover (you have to willingly try to cover the antenna).
Of course, there are style cues that you cannot use with such a placement and material, it’s hard to do brushed aluminum/metal skins with plastic, and you have to move some features (like the rear speaker and camera) a bit lower than you’d normally like. And you cannot do those ultra-thin edges (because the antenna is close to the edge). But at least it does function number one of a phone - make a phone call!