BryonD
Hero
So again the held guy in plate and the held guy in a robe are no different.Thus: if there's enough question that you need to roll a die, then Dex bonus applies. At the point where you'd be denied Dex, no roll is necessary.
I agree it is a corner case. But the OP is in that corner, so for on topic, it matters.
It actually came up in my game last night. And yes, that is a really rare thing, so just a funny coincidence here. A full plate fighter was held and an attack roll came up 4 and 6. I ruled it a clank.
The fighter in question had a DEX of 10, so the true point of this thread didn't play in. But this does address your point.
The fighter remained held for a couple more rounds, and didn't stay so lucky.