Both in posts from Divisortheory on BG, and verified by myself to check the exact defense ratio, as I've been going through perfect setups on various mobs for our HNMLS so that we can streamline gear.
This is the link from Divisortheory:
http://www.bluegartrls.com/forum/viewtopic.php?t=16214
In my OCD'ness I've made huge posts on my LS forums exactly on how things work (mostly for Thf's trying to force up TA damage on Fafnir/et all.. but that's another story).
I've got Ultima in an hour, but I'll do it straight afterwards - give myself some odd gearings and hopefully be able to prove it to you. Then, if you'll believe that, I'll do the same for the Assassin's Legs/Andravanauts post on the Thf side of things.
I realise my tone isn't always shiny, but I don't say stuff deliberately that's wrong. So sorry if I upset you.
If you want to test it yourself on Colibri, it's fairly easy to as well, just use gear swaps and /check.
Remember:
/check will display the ratio without taking into account Level Correction function
If AttackDefenseRatio < 1.00 → High Defense
If AttackDefenseRatio > 1.25 → Low Defense
Other ratio range → No defense info displayed
P.S. I'm going to assume that sig is out of date for your job levels. As a melee, you should know that Madrigal + Sushi is relatively pointless if you're using a decent setup. Not that it'll change your mind much.