Is the dice system too generous for my rpg?

I’m writing my paper RPG that sets up in a modern day world, with elite soldiers facing several horrific situations. I wanted to create a game system not too complicated, but not too simple and somewhat original (I’m thinking about the chaosium system, really simple to understand, but seen in 90% of the games edited in my country).

I wanted to inspire myself from a CYD system, where the system relies on the possibility of choosing between using a d10 and getting only results from 1 to 10, or a d20 and having a critic on 20, fumble on 1 and 11, and every other odd number count for zero. It’s made for risk taking, and trying actions you’re not supposed to succeed in normal times.

So, for my system, as I need to make things a little bit different not to be called out for plagiarism, I was thinking about using the system of calm and stressful/improvised situations. If a player wants to make something by taking their time, they use the normal dice, if they are in a stressful or want to try to improvise they use the other.

For example, if the characters need to climb a wall, if they want to climb by taking their time and are not stressed by the environment (rain, vilains, etc.), they just throw the normal die. If they feel adventurous, and want to go faster than the normal way (or if their competence score is too low to succeed with the normal dice), they can thrown 2d8 aka stressful dice. They can thus make a splendid success if they’re lucky, or miserably fail and fall. If they’re surrounded by ennemis and have to get quickly up the hill, they must throw the stressful dice.
Another example can be the same for fights: if the players have the advantage, they can choose what die to throw. If they’re surrounded or in direct danger, they have to use a stressful throw.

In the first version, I used a d12 for the normal, and 2d8 for the stressful, where (1-1) is a fumble, (8-8) a critic, and all other doubles count for 0. The problem is, for my first test game, my players never used the stressful dice. They never thought that they really needed to use it, and that the difference (13 to 16) wasn’t worth enough the risk.

So I wanted to change, and use a d10 for the normal, and keep the 2d8 for stressful. 6 as a gap difference feels maybe worthier, but now I’m wondering if the doubles wouldn’t be too generous: is 64 possibilities of rolls, there are only 6 possibilities of having a 0, and 1 with a fumble. Compared to that, the original CYD system as a 1/2 success rate. I feel this one is too harsh, and mine is too generous.

After the dice are thrown, you add the results to your competences (comprised between 0 and 5), and have to be above a certain threshold of difficulty (5 for easy, 10 medium, 15 hard, 20 very hard, 25 impossible (not definitive, but you get the idea)).

Does anyone has any idea to improve the balancing? I wanted to use the double system for fail because it’s easy to see at first glance if you succeeded or not, rather than making calculations.

Thanks a lot if you’ve read everything!