Because I felt bad, I actually looked into it. In a highly un scientific way I took both charts, put them on the exact same time scale (the full life of AM100) fucked around in photoshop and came out with this in 20 seconds. http://imgur.com/wKeR9Fb
Initially AM1 (full shares) trade at a premium, many people were not happy with the fee TAT took on these shares. It seems like people could care less about that fee now, as the difference between the prices is so little it is hardly there... in fact for some points in time fractional shares are above full shares.
Mind posting a link to the relevant auctions?