on your model:
i get 105 rage, HS now costs 120% or 36. I have only "lost" 1 rage. but for that rage i get 10% bonus damage for it.
on my model:
you have 105 rage, you use any attack but HS or cleave and they cost exactly the same and have the same results, IE no bonus, you just get to use some rage you would have otherwise lost.
If you choose to use HS, you get 2.5% extra damage and it costs you 35 rage total to do it.
The difference is, every second you try to horde rage, you lose some, 10% of everything above 100 (call it minimum 1 rage) so hording is really no easier.
at the end of the above examples: you have 69 rage and did 10% bonus damage. I have 70 rage and did 2.5% bonus damage.
Now lets look at non-HS/cleave at 110 rage.
you use devastate, 15 rage becomes 21, and you get 20% bonus damage.
I use devastate, 51 rage stays the same, no damage bonus.
you end at 89 rage and do 20%
I end at 94-95 and do 0%
Yes, i can "keep" more rage, but thats all i am doing. and thats the whole point, that we not throw away a burst of rage gained.