That OT 30 min nap where you can resettle might actually be UT, not all UT naps are happy wake ups and not all are unable to be re-settled. Mine had a period of UT naps, waking screaming, able to resettle with work, looked typically OT but was UT, an A increase made him good and tired enough to transition on his own, get a better nap and wake later and more rested. I know it kind of goes against how OT and UT naps tend to look but when you take into account the A time being low too, well, changing the scene or toy to prevent boredom and lengthen the A might actually give you a better nap.
It's worth noting too that they can begin to prepare themselves for a nap habitually, so fussing when they know they get a nap as they are getting ready for it. it can take a few days to get out of that habit into a longer A.