HSA Contribution

Hi, I have a question pertaining to doing a after tax HSA contribution to lower my taxes.  I have 2 separate HSAs. One from my old employer and one from my current employer both. I contributed 2400 in total on the my current employer HSA (my contribution and employer total). I want to contribute to the old employer HSA since no contributions can be made pretax. When I entered the amount of $4000 my taxes due only reduced by about $900. Wouldn't the full $4000 come out of the calculated tax due? Is there somewhere specific I need to add it in turbotax for it to calculate correctly?

 

Any insight would be appreciated. Thanks