damn. didn't work out. I CAN make it successfully import my Det-Tax Amount but the method, although it yields an identical look on the screen, fails to post based on the totals not working out.
According the quote from the manual it should allow me to import my own tax value unless I leave it at zero in which case the calculation associated with the distribution code takes over. However, if I make the distribution code for Tax In Purchase it ignores the amount I import for Det-Tax Amount and puts in the calculated amount.
Seems buggy to me.