I'd say small fish mate,usually with the method if big fish are attacking it you will get a lot more than the bobbin just rising and after a while it would just tear off.
Try using a 2 inch hook link and leave your hook bait outside of the ball , it's worked for me in the past when I've been getting a lot of twiches but no runs.
Also try to match your hook bait to what's in the mix, if using corn in the mix then use a single piece of corn on the hair.
Ive had some good days using a lot of chickpeas and corn in the mix and then alternating the hook bait between the two.
One other thing is you WILL pick up small fish as well.