When we daven mincha, we say the psalm we call "Ashrei" first. This seems to come from The shulchan aruch, O"C 93:2. This section requires that the amida be "samuch" to the psalm.
We say kaddish after the psalm. Why isn't this a hefsek? I was reading some of the related questions regarding kaddish in maariv. Amidst all the questions and answers was this which says that the kaddish is not a hefsek because its content echoes the geulah requirement.
[other resources: Answering "Brich hu" to the kaddish before shemone esrei at maariv and https://judaism.stackexchange.com/a/36259/1362 which posits that the kaddish allowed because maariv is optional]
If the smichut is not geulah based in mincha, how can we say kaddish there without its being a hefsek?
The Mishnah Brurah writes in 108:2 (13) that one davening a make-up amida should insert ashrei before the second one to ensure the proper smichut, but earlier, the mechaber wrote in 105 that the break between 2 prayers should be very short in order to maintain the right mindset. In the end of (13) it seems that the M"B says that 105 is a bediavad case and 108 is lechatchilah.
What is the general rule about smichut in mincha and how does kaddish fit in?