Yes it's hard when they're distracted! With the feeds getting shorter, it's possible that he may just be getting more efficient - do you think he might be? Also, it's possible that he may not need feeding quite as frequently as he used to - some LOs will move towards a 4 hourly feeding routine by 4mo, however others don't ever manage that stretch during the day so I'm not saying you should push him, just that you may find if you feed him a little later after his previous feed then he may be hungrier and more willing to feed? Mine responded quite well to singing whilst feeding, it sometimes calmed them down - or fiddling with a necklace or something.