still missing it. when you say 2D TC, it means 2D resoltion.
resoltion is what defines what you divide your running count by - if you are using 2D TC resolution, that means you divide by the number of 2D segments remaining. you might use that with 1/2 deck estimation (you round what you see as remaining to be dealt down to the nearest half deck), which means you estimate the number of 2D segments remaining down to the nearest half deck.
let's use your example - a 2D game. at the begining before any cards are dealt, your TC denominator would be 1, since there is one 2D segment left. after 1 deck has been dealt, your denominator is now 1/2 since there is only 1/2 of a 2D segment remaining (ie 1/2*2 = 1Deck remaining). this is resolution.
comparison between 1D and 2D resoltion -
in a 2 deck game, before any cards are dealt: using 1D resolution, your denominator would be 2 (since there are 2 1D segments remaining). using 2D resolution, your denominator would be 1 since there is 1 2D segment remaining.
now lets explore estimation - now lets say almost 1.5 decks have been dealt. instead of rounding this down in your estimation to only 1Deck remaining and using 1/2 as your denominator in your TC calculation, you do the following: you round to the nearest half deck and say, ok, 1.5 decks have been dealt, meaning 3/4 of a 2D segment have been dealt and only 1/4 of a 2D segment remains (1/4*2D = 0.5D remaining). so now i would use 1/4 as my denominator in my TC calculation.
so to compare estimations: if 1.4 decks have been dealt and you were using 1D estimation, your denominator would be 1/2 but if you were using half deck estimation you would use 1/4 as your denominator.
make any sense?