Ladies and gents, in case you are wondering (as I was) which battle Hong Taji was referring to in EP 14 (34’39 mn of 1’28’53 mn) I did again some digging. I haven’t found any precise information yet about which battle at mount Song he refers to (when it took place exactly in 1643) but I found some interesting info re the fact that they were fighting the Ming at the southeastward point in the Ming Empire: my feeling is that it was due to the fact that it is one of the five mythical mountains (or rather mountain ranges) of China, with huge symbolic meaning. Songshan is a sacred place of Chinese Taoism, the birthplace of Buddhism where the Shaolin Temple is located, and the birthplace of Chinese Neo-Confucianism.
I am adding the names of the five mountains/mountain ranges and a screen cut-out from Korean Wikipedia with their names. So here is :
숭산 / 嵩山 wikipedia KO : https://ko.wikipedia.org/wiki/숭산_(산) [Song Shan]
항산 / 恒山 wikipedia KO : https://ko.wikipedia.org/wiki/항산 [Heng Shan]
태산 / 泰山 wikipedia KO : https://ko.wikipedia.org/wiki/태산 [Tai Shan]
화산 / 華山 wikipedia KO : https://ko.wikipedia.org/wiki/화산_(중국) [Hua Shan]
형산 / 衡山 wikipedia KO : https://ko.wikipedia.org/wiki/형산 [Heng Shan ; same English transliteration but different Chinese ideogramme]

In a way they form a five-pointed star pattern, if you look at the map. Possibly representing the five elements … but I have not looked into the mythological/symbolic meaning of the mountains in China ; I did some of that for Korea, when I researched Jirisan for example. Korea took over the Chinese cultural concept of the five mountains with mythological/symbolic meanings (the concept is represented in the screen backdrop which you see often behind the Joseon King in the Throne Room).