Form 1116 Line 1a : Question for Long term captial gain

I received the inherited house in the foreign country and paid a tax for the long term capital tax in foreign country and USA.  I used TT, got the foreign tax credit.  I looked very carefully the line 1a, could not figure out.  It was subject to LTCG tax 15% and 20%.

Simply 1a is from Sch D tax wks line 30 (15%) x 0.4054 plus line 33 (20%) x 0.5405.  Then this is about 4.5% lower than 1a from TT. I had ver small expense and very small foreign tax paid on the dividends.  These are so small, I do not think affecting like 4.5% difference.

How to figure out 1a?