I found the answer once I got a book in game that had the rune recipes.
Medium rune = small rune + small rune + pixie dust.
The rune recipe pages that I found online had not mentioned pixie dust is also required to combine runes. I guess I need to find more stardust plants. I have only found one in the wild so far, and one on a vendor....and I use alt-key everyone to scan for stuff since my main char has TK3 so can easily grab stuff from all over current area.
