Both the psyllium's I've used have either been 1 heaped teaspoon or 2 level teaspoons. 2 tablespoons sounds like *a lot* of psyllium. If the person doesn't drink enough water to go with this (which will be quite a lot) they are likely to jam themselves up further.
Flax is altogether more gentle on the body, so I'm not surprised you use it.
Where did you read/hear about 2 tablespoons being used and have you tried it?