Hi there
I wouldn't cut the awake time at all, it's already very short for age (especially if you are not always achieving the 3hr 15 or 3hr 30 you are planning for).
Being sad when he wakes, as you describe, can sometimes be due to UT (under tired) for naps. People often think that an UT baby will wake happy and an OT one will wake unhappy but that's not always the case. My DS would be unhappy waking from an UT nap because he still needed more sleep but was not tired enough to transition between the sleep cycles due to being put down too early. So I've had experience of that.
No, A times are not just based on an 11hr night. Mine only did a 10.5hr night and his A times were far longer than the A times in guidance but as you will know in the guidance it says "some are getting more".
Mine generally needed the full A times even after a broken night it was extremely rare to need a shorter A time and really that would only be through the worst night of teething or very bad illness.
Sounds to me more like he needs a longer A time, perhaps for one nap to be long and one to be shorter.
LOs don't always happily shift A times, they get used to going to nap too early so keep on doing it but it isn't always good for them.
Hope that helps