I can't answer your question because your reasoning for the truncated values are correct. If the indices are for truncating and the standing index is -1 you stand at any TC -1.9999 or higher.
For newer players Tthree reference to standing at -1.9999 or higher just to clarify the meaning of higher -1.9998 in this instance is higher and at -2.0000 is lower and you would hit the hand.
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