Fairtex SP5 rubbing against my Achilles area any advice?

Hey everyone!

I recently bought a pair of Fairtex SP5 shin guards, and after just a few training sessions, I've been having an issue with the back of the guards rubbing against the area just above my heel, around the Achilles tendon.

Both ankles get red and irritated after training, almost like a friction burn. I've tried wearing ankle supports underneath, and they seem to help a little, but it's hard to tell for sure while the skin is still irritated.

Since the shin guards are still relatively new, I'm wondering if the material will soften up with use, or if this is simply a fit issue. Any advice would be appreciated thanks in advance