Why won't he stand up to her???

Our little d'uccle roo is about 3 yrs. old. He's with four big girls, all almost 2. He's been with them since last summer, and after his quarantine period, it took him all of 5 minutes to assert his authority (despite him being 1/3 their size); they accepted him pretty much from the get-go. All will at least halfway squat for him (although he's generally up at the shoulder area). He treats them well, calls them for treats, does all of the "good roo" things.
But for the past two or three weeks, I've noticed my buff orp girl going after him, a few times after he jumped on her to mate, but more often lately she goes after him when food is involved, and sometimes for no reason that I can see. She's got him good a few times, grabbed his comb, and sent him squawking.
My question is, why does he not retaliate?? I know she's got several pounds on him, but she's at the bottom of the pecking order with my girls, and I've seen him (last year) put my lead hen "in her place." So why do you think he's allowing my buff girl to push him around????

The two birds in question:

 

Okay guys...thanks! I know she's an amazon compared to him, but I still think he's "allowing" her to behave that way, and I guess I was just wondering why. His poor comb looked really bad last week where she'd gotten hold of it. Just trying to figure out chicken thinking...