The diameter of the Waffle is smaller than all other 1/10 Raw Speed rear tires. This means that the rear inserts are a little oversized for these tires. If the full non modified insert is used, the Waffle will be very full and have a relatively hard feel to it. This hard of a tire will work on very high traction conditions but will struggle on low to medium traction conditions.
It is highly recommended (for low to medium traction conditions) that you trim the inserts to make them a little smaller so that the tire does not have such a hard feel.
A couple very popular ways of making inserts softer is to either punch holes in the inserts or to turn the insert inside out and trim the inner ridges/flutes down a little. It is recommended that you trim little sections at a time and put the insert in the tire and the tire back on the wheel and check the firmness until you have achieved the desired feel.