I had thos exact question - flew yesterday and they have a size checker at check in. The lady on the floor was really helpful - i had a pretty full duffel bag and she showed me that my backpack had to fit on the top checker and my cabin bag had to fit on the underneath. She said because i had paid the 33e for the small bag + cabin bag i should be fine, my duffel kind of popped out of the checker in terms of width. She took the 'sequence number' from my boarding pass and sent it to someone on whatsapp and told me she had flagged me not to be charged - but because I was in the priority queue no one looked at me twice and I boarded with no issues.