Chopping nuts evenly is a challenge. Even with a good knife and cutting board, it is difficult to get the nuts to an even size without being outrageously fussy about it and wasting the afternoon.
you have found, you face the same problem in the food processor – by the time the largest pieces are chopped enough, some others have been reduced to powder. In our experience, pulsing relatively small quantities in very short bursts works the best. When we’re being especially fussy, we stop pulsing one batch when many of the nuts are the right size, pour the nuts into a separate bowl and pick out the nuts that are still too large and add them to the next batch.
The more cooking we do, the less we care whether the nuts are more or less the same size.