iPhone 16/Zenfone/13 Mini (in mm)
Height: 147.6/146.5/131.5 - the mini is 15mm shorter than the Zenfone which is only 1.1mm shorter than an iPhone.
Width: 71.6/68.1/64.2 - the mini is 3.9mm thinner than the Zenfone which is 3.5mm thinner than an iPhone
Depth: 7.8/9.4/7.7 - the Zenfone is significantly thicker than the iPhones.
Volume: 82.4/93.8/65.0 cubic cm - the Zenfone is physically larger than an iPhone 16 by a decent margin.
The Zenfone simply isn't close to an iPhone mini size. It's larger than an iPhone by volume and the depth does matter when holding it. If we're talking about front-edge to opposite front-edge, we're talking about 87.2mm for the iPhone vs 86.9mm for the Zenfone and 79.6 for the Mini. The Zenfone saves you 0.3mm in grip-distance over an iPhone, but a Mini saves you 7.6mm in grip-distance.
Heck, let's look at weight. A Zenfone is 172g, iPhone 170g, iPhone mini 141g. The Zenfone is the heaviest of the three.
One of the big limiting factors for Android phone manufacturers is the battery. iOS is a ton more efficient. The Zenfone is thicker to accommodate a 4300mAh battery compared to the iPhone 16's 3561mAh (21% larger battery). And the Zenfone's battery is kinda small by Android standards.
People often don't think about the challenges of making a small phone. The electronics don't shrink. If you need a certain square mm for those electronics, they take up a larger percentage of the interior on your mini. You don't need as large a battery because the screen it is powering is smaller, but not proportional to its size - you're still drawing the same power for all the electronics. So you have a smaller percentage of interior space for the battery and you need a larger battery relative to the interior space - or you need to sacrifice battery life as Apple did with the mini.
For example, the iPhone 13 mini is 84.4 sq cm and has a 2438mAh battery. The iPhone 13 is 104.9 sq cm with a 3240mAh battery. The iPhone 13 is 24% larger, but can accommodate a 33% larger battery - because the electronics take up basically the same space regardless of form factor.
So to make an Android mini, you'd be sacrificing a lot of battery life. The Zenfone is not a mini. Its grip-size is basically identical to an iPhone. In every way, it's much more an iPhone than a mini.
iPhone 6S: 138.3/67.1/7.1 = 65.9 cc the mini is just barely smaller.
iPhone 4S: 115.2/58.6/9.3 = 62.8 cc smaller than the mini.
Treo 650: 113/59/23 = 153 cc which is about the same volume as a Galaxy Z Fold 3... the displacement was so uncomfortable, people often used hip holsters for the former.