So, both those vowels are very similar, the only difference being that [a] is made when the mouth is fully open while [ɐ] is near-open.
Both those sounds exist in my language (Brazilian Portuguese), so I'm a little confused because while normally I would hear [a], I feel like sometimes I also hear [ɐ].
I believe it happens only with some specific people that may speak with their mouths less open than the average, but I might be wrong.
Does anyone have any input on this? Or maybe studies or papers that explore this matter? I've found some stuff about the Korean language, but not for Japanese.