In the Optional Rules section of the core book there is a section on modifying abilities. A selection of it reads:
For any Intellect ability with a specific range, you can increase the range by using more mental energy. If you spend 1 additional Intellect point, you can change the range by one step—either from short to long, or from long to 500 feet (152 m). You can’t increase a range beyond 500 feet by spending more points...
...A player can make a special roll to modify the range, area, or other aspects of an ability. The roll is always modified by the stat it’s normally based on. The GM sets the difficulty for the roll based on the degree of modification. Like any roll, the player can use Effort, skill, and assets to reduce the difficulty. Generally, the difficulty falls into one of three categories:
Impossible (modifying an ability to accomplish an effect that has nothing to do with its description or intent)
Formidable(modifying an ability to do something similar to the description or intent, but changing its nature)
Difficult (modifying an ability to do something within the spirit and general idea of the ability)
(Numenara, core book pg. 114)
I have a player who has been using the Far Step esotery while spending one more from their Int pool to be able to move 500 ft in a single round regularly. I had been letting this go on but it has caused issues and upon rereading the rules I believe the second paragraph is relevant and they would need to make an Int check (difficult) every time they wanted to make use of this rule, they however believe that this is only require if they wanted to modify the esotery in a more involved way such as using it on another character instead of themselves.
My question is whether or not this roll needs to be made for all modifications or only ones that affect more than range or duration.