Seeking Confirmation On A Northern Song Dynasty Cash

Hi. This one came from my "trash" pile of unattributed coins.

I'm quite sure that the first character is Tian, which would push this into Northern Song territory (under Emperor Zhen Zong). In looking at Hartill, I'm a little torn between attributing this as 16.70 or 16.71, with the difference being that the first variant has straight feet on the bao, while the second variant has smaller characters and two dots on the left side of the tong character. Unfortunately, the coin is so worn, that it is difficult to know whether the tong originally had one or two dots, but currently there are not two dots. On the other hand, the line drawings in Hartill seem to indicate that the first variant is a mm or two larger in diameter than the second variant. My coin is definitely on the small side--a little smaller than the line drawing on the second variant.

So my question is...should I attribute my coin following the shape of the tong (16.70) or the diameter of the line drawing (16.71)? I know that a thousand bazillion coins were cast during the Northern Song Dynasty and Hartill only includes "a few of the more distinctive varieties".