I remember mine had inconsistent A time when he was tiny. Sometimes he'd seem ready for a nap and would happily go down in his travel cot (in the family room) but then just stare for ages, no fussing, quite content but just not sleep. Sometimes after an hour or so he'd nod off, I generally just thought it was a step towards independent sleeping for him to be able to lie there watching and listening and nod off in his own time. Also sometimes he'd sleep for a bit, wake but not fuss and then do the watching and listening for ages and eventually nod off again.
I also remember at around 4 months when I found the forums (when he'd started taking short naps) I was still following cues and his first A time was long and the rest shorter. I tried for quite a while to reduce the first A time because obviously he was above guidance times and rather than cue following I was looking more at suitable routine times, it turned out he needed longer rather than shorter and he always had that super long first A time right up to dropping the nap completely. It's just his way.
I really wouldn't worry if he seems to be ok with it. No point stressing yourself over A times from such a young age, not unless there is a problem. xx