There are a variety of meforshim who offer similiar explainations that adding the extra month during Adar in a lunar calendar cycle is because chodesh Nisan is the “beginning” of the months making chodesh Adar the last, and chodesh Tishri the seventh month. Thus, logically, given the need to keep the lunar calendar in cycle with the seasonal cycles of the Gregorian calendar, we add the “extra” month after the last month (aka Adar rishon and the extra Adar sheni).
