won first match by 16 rounds in 2 maps total.
lost second match by 8 rounds in 3 maps total.
lost third match by 4 rounds in 2 maps total.
(16-8-4) = +4
4 of HL matches finished with only a two round diff, 3 losses and 1 victory
the other 3 were a loss with 8 RD, and two wins with 10 RD and 6 RD
If you do the maths it goes -2-2-2+2-8+10+6 = 4