Reverse D20ish system?

(Using standard D20 ability scores and values)

Attack is a static number (like Ac)
Defense is a dice size (Like weapon damage)
Wounds are your Hit Points. They are generally 10 or lower.

Example #1:
Player 1 attacks and deals 5 damage to player 2.
Player 2 has a d8 defense dice. He rolls a 4 and only takes 1 damage.


Example #2:
Player 1 attacks and deals 5 damage to player 2.
Player 2 has a d8 defense dice. He rolls a 7 and takes no damage.



Attack values range from 1-10
Defense dice size range from d4-d12 (d4, d6, d8, d10, d12)
Wounds range from 5 (starting) to 10 (maximum)

To increase a attack by 1 it costs 1 training point. (Cap 10)
To increase a dice size in defense it costs 2 training points. (Cap d12)
To increase your total wounds by 1 it costs 1 training point. (Cap 10)




Design Notes:
Minimum dice sizes are where chosen so that they would be higher on average (and at cap).
Maximum values where chosen so that the spread between min and max where not very large.



Options:
Damage mitigation (like damage reduction or simply armor) could provide a damage threshold. Damage under 2 is ignored for example. If they take OVER 2 damage at one time, their armor is useless until repaired and does not factor into the fight anymore.
Dice sizes can be effortlessly converted to percent values or random number generation.