No, it's the other way around. For subjects with a higher/foundation paper, on the higher paper, the grade boundaries for a 4/5/6 will be lower.
The paper is much harder, so everyone is expected to get lower marks, and a 4 is the lowest possible grade. The paper doesn't assess grade 1/2/3 content. Obviously grade boundaries vary, but on a higher chemistry paper, basically only question 1 and 2 are assessing grade 4/5 (standard demand) and the rest is assessing 6-9 (higher demand). Therefore, arguably, you should only need to get 16% to get a 4, 33% to get a 5, and so on.
For a paper that's assessing the whole grade range, from 1-9, you need to assess those getting grades 1, 2 and 3 as well.
Therefore e.g. 11% could get you a 1, 22% a 2, 33% a 3 (I know it doesn't work exactly like this) but you can see it would push grades 4/5/6 much higher.
It shouldn't be easier to get a grade 6 in English lit than in Chemistry.
I'm not sure I've explained this well, but hopefully it makes sense?