I don't know if theres another way to find out how much he earns.
The CSA would make him pay 15% of his take home wage. �190 is 15% of �1266 (? correct me if im wrong, my maths are pants). So maybe that helps you gauge if he should be paying more, but I suppose only if you have a rough idea of what he earns. Be wary of going down the CSA route as unless the absent parent is co-operative they are absolutely useless. Also if the award they make is less than what he gives you now you may find yourself worse off.