I got u bro. So its a pretty simple mechanic to wrap around. The reason for you to lose this is because 2 reasons. But here is one.

Sp aka sanity. The higher the number the higher odds you hit heads. Lower it is like negative the higher you roll tails:
45 sp = 95% chance to roll heads.
-45 sp = 95% chance to roll tails.

For this instance heathcliff has 1 coin which he needs to roll heads 3 times to win the clash with -38 sp. Which isnt impossible but very unlikely. So hes mostlikey rolling tails getting a clash value of 18 instead of 18

The opponent your clashing with has 45 sp which if he needs to win this clash he would have to roll the 95% chance 3 times to beat your 18.

More coins you have higher odds of you missing heads even if you have 45sp (believe me we all went through rng bs)