I don't think it matters and you should even get up to do walking meditation if you notice the hindrance of drowsiness, it s not the go-to adjustment but it's definitely one of the things one can do to wake oneself up. See Capala Sutta
The question i would ask is whether adjusting posture is solving your issue because it's probably better to attend to a different theme.
In general i think one of the biggest mistakes is to sit observing the hindrances.
It's not an easy subject to advice on because what one at that time should do depends on what one can do and in that we are all limited by our general knowledge.
I generally counter hindrances by picking themes and making adjustments. Commentary even lists 'tiresome work' as a remedy for drowsiness, not something id recommend but i favor it over nodding aimlessly for half an hour.
If one just has one theme be it development of samadhi which leads to mindfulness & alertness, metta, maranasati, the practise of stilling the breath or the development of other perceptions; if one just does one thing then it is going to be a hit or miss most days and maybe by virtue of general development one might overcome the hindrances at some point but afaik it's not what the Buddha recommends as he taught directed and undirected development.