@RiotScruffy/Meddler/Xypherous/etc. - How do you scale damage ratios on an armor-scaling tank?

Rammus, Taric and Malphite all get bonus damage via their armor, but at very small percentages. I'm trying to develop another armor tank Champion (who would also give the tanks another female to the roster), but I've set her ratios much higher than the aforementioned Champions.

Reasons? Firstly, she does primarily physical damage, not magic, and has no access to armor penetration (no AD ratios, so Black Cleaver and Last Whisper suck on her). Second, unlike the above, she can't increase her own armor via an ability; her defensive ability is a damage-absorbing shield. As such, she can't reach the same levels of armor as Rammus, Malphite or Taric (i.e. she can't get within the 400-armor ranges easily).

For those reasons, her armor ratios are 30% on her Q and 25% on her W, respectively, while her passive (which normally requires her to get attacked first) has a whopping 60% total armor ratio. Unfortunately, without the ability to test numbers in a PBE environment, trying to balance out the numbers is hard. I don't want the Champion in question to be ignorable when she builds 250-300 armor, but at the same time she can't become a super-bruiser as a result of said build.

I've posted the concept in Community Creations, so here's a link: http://boards.na.leagueoflegends.com/en/c/fancreations/25lAeiAZ-yousoconcept-nephree-the-dark-crusader

Any advice you could give?