(non) contributory pensions and earnings

I have a contributory pension that is not the full amount and wonder whether I should apply for the full amount as a non contributory pension instead.

As I go through the form 11 (using the calculate button for potential income/pension values) it sees to me that any (smallish) increase in the pension earning is likely to be be more than offset by the increase in tax payable.

Am I seeing things or is there indeed some kind of a barrier to realistically earning money on top of one's pension (in a self employed capacity)?

You can earn as much as you like on a contributory pension but you must pay tax. A non contributory pension is means tested and you are supposed to notify Social Protection of any change in your means - if you do not , anything overpaid to you will be taken out of your estate when you go to your eternal reward. This is very common for people on non contributory pensions and I am aware of a few people who had to pay back several thousand from the estate of their parents.