So I bought cloth pads and became quickly smitten with them. So I've used them for a while. I tried the cup a few times with no great success.
But last night I tried again, and used the punch-down fold instead of the c-fold which I usually use (I've found in the past the punch-down doesn't always pop open properly). I don't know why it took me this long to try another fold, perhaps because I found the pads to be so awesome as well.
Now my cup is perfectly comfortable and non-leaky again! Success!