Per the sleep expert Dr. Weissbluth, only 18% of babies actually take a catnap at 6 months or older. Even in Tracy's books, they are absent of the catnap as well. Depending on the timing of DD's two naps, I try to get her some quiet time. Most of the time it is between 5 - 6. I will either let her quietly play in her crib with the lights off and a few choice pastel stuffed animals, or we'll go for a walk, or we'll sit and read. I've found that this will give her some rest without actually getting sleep. Every now and then she has been known to fall asleep in the stroller. If she doesnt' seem to get too much rest, then I'll put her to bed 30 minutes early. 30 minutes is the magic number with us. Any more than that will result in an earlier wake up.
I go with the flow more on the eating. occaisionally, we'll have a 5 hr EASY in the afternoon since the nap was a little longer followed by a 3 hr EASY. She seems to go wtih the flow.
Hopefully when your DS is a wee bit older and he can go for longer A times, he won't be as cranky by the late afternoon and the afternoon nap will get adjusted (hence our 5 hr EASY!)
HTH!