http://bulbapedia.bulbagarden.net/wi...ming_IV_glitch
It's been a while, but I stumbled upon the explanation for this today. Unlike what we thought, it doesn't just roll the Attack to 7 if the "real" IV is higher. To clarify, Roamer IVs can stem from any of the following combos:
0 -> 0, 8, 16, 24
1 -> 1, 9, 17, 25
2 -> 2, 10, 18, 26
3 -> 3, 11, 19, 27
4 -> 4, 12, 20, 28
5 -> 5, 13, 21, 29
6 -> 6, 14, 22, 30
7 -> 7, 15, 23, 31
That helps narrow down your possibilities when you look at the Attack stat of the roamer you capture. Obviously the others will be bad.