It works because both of those fighters have excellent Footwork, like Anderson Silva.
To get inside you really shouldn't be eating punches. Cover their lead hand, or move your head as they jab, and step in.Tucked chin is pretty ideal in general because it pre-emptively braces the muscles of your neck to reduce the impact of the blow if you get clipped. I almost never use the gloves to defend but I always dip my chin. Usually chin-tucked = guy focuses on head movement, whereas a more upright fighter focuses on using feet as defense, but I try to combine the two. On the other hand (pun not intended), "hands up" is NEVER enough because gloves really aren't meant to block punches, but rather, protect the hands. Of course it works in situations where you use boxing gloves, etc. but it's a bad habit to get into because it freezes you bolt-upright in front of them and makes it harder to counter, which footwork/head movement doesn't, and in fact makes it easier to do so.
People will say, "if your hands are up a punch that lands will be softened!" and while that is true, if one was moving the head or using the feet correctly, it never would have landed in the first place. Like, why do I need to block a punch that I could've evaded by simply ending my combination with angling footwork (1-2-step out-pivot), etc...?
Basically a lot of fighters just try to get by with illegitimate modes of defense because they aren't taught or trained any better. Stefan Struve is a good example, he only tries to cover up and it never helps because he always gets lit the fuck up even in fights that he wins, and Mark Hunt regularly hooked around his gloves every time he covered.
But, I do like to hold the phone while throwing low kicks and hooks for sure, because it provides the threat of a hand destruction + allows one to cover their chin, temple AND back of the ear while striking.
