The way the stats are lowered is simply substituting the level in the stat formula for 50, for example a Shuckle with 31 ivs and 252 evs and a neutral nature in defence would have these defence stats at each level:

Level 50 = ((31+(2x220)+(252/4))x50)/100)+5 =272

Level 100 = ((31+(2x220)+(252/4))x50)/100)+5 = 539

And 539 is not twice 272, which is why even though you have the same ivs and evs, your stats may appear unfairly adapted. The thing is, as long as all stats are adapted in the same way no side comes off worse off. To put it simply, if your stats are 30 and there's is 60 it doesn't matter whether you change this to 15&30 or 10&20, it's still the same ratio