Any advice on which size to buy?

I've been getting XXX for years and pairing with the provost apple on top, tinfoil, and alpaca mini rook. This was fine but I recently upgraded to the Gravyl bowl and my two XXX coals are dying out before my tobacco is spent. I was thinking I need 3 coals to have a full smoke and I wasn't sure if I should get the quarter circle or the 26 big cubes. Thanks.