Preventing the icon from resizing while maintaining it’s position is a bit tricky.
Create a group — call it “container”. Within it, create a rectangle that touches the top edge of the artboard, but not the bottom. Then also put the icon you want to maintain it’s position within the group. Give the group the resize property “Pin to corner” and you should be good to go!
There are some more tips here: https://medium.com/sketch-app-sources/sketch-39-resizing-cheat-sheet-feec0450e7e2#.tylrzip3x
Hope that helps!