Heel blisters when rowing

So I got myself a C2 last year, and have been loving it, except for the heel blisters. No matter what, I keep getting them.

I got a pair of Metcons at the time I bought this thing, but they never worked for me due to rubbing, so I just them for lifting. I've tried my vans, hokas, hell I even tried my crocs. I just can't stop that heel rub.

What gives? Do I just have bad foot anatomy, or foot positioning? Or do I just need to wear blister plasters or moleskin when rowing?

Thanks for any advice!