Hi I'm back to chime in!!
My lo first nap (when his WU is normal and I caught it. Sometimes he EWs and won't resettle or wakes and I don't know as he wont call me and is just there haha. I usually suspect ar least had been up for 10-15. He's in our room too! He just wakes quietly some days!) is at 1.5 A time! It seems to get me at least an hour lately. Again, assuming our WU time is more balanced. So as it was mentioned, some pushing can help? Mine is 10 weeks old; a week younger. Maybe you can try 1hr 15? If it was a good WU and rested. I notice if he does anything less than a 1.5 nap, the next A time works at 1 hr. Then if that was at least 1 hr, he's pretty happy and the next can extend again a bit but only to 1 hr 15.
I go by how he's feeling. Depends his nights too... Some mornings after rubbish EWs or unknown exact WU time he's already OT come normal hours and then the whole day is OFF.
I have to agree that if it's all bad short naps of 20 mins, something might be causing discomfort. I say this bc the past week I've posted about the same issues (fighting swaddle, resisting naps, Unknown A times etc..as I told you above) and come to realize Monday, he has a tummy bug. He's been pooing' round the clock. It concerned me as it can dehydrate them and all that... Today, he went back to decent naps (not prefect! Hehe)
I had my MIL with me and I was able to focus 100 on him and get him rested as he's been Sooo OT lately from discomfort! ...and I focused on proper A times and it worked out. As we approach 3 months A times need to gradually get closer to 2 hrs which comes at 4 months.. Yk? I mean from what I've seen on BW and advised from the great moms/moderators here too!