Position the accordion on its legs is OK for the right hand reedblocks but as can be seen in this sectional view of the accordion, the reedblock identified 2 of the basses (left hand) is quite tilted.
The leather skins under this reedblock will tend to fall downwards when the accordion is held on its feet.
It is for this reason that it is preferable to store your accordion on its side, in playing position.
In this position ALL the skins will be kept on the side and will have less tendency to deform.
Moreover, there are transport cases for accordion with feet on the side.
Besides, I'm not even talking about accordions with a tone chamber (cassotto) which have some of their reeds horizontal when the accordion is held on its legs!
We recognize by ear a problem of deformed leather skins when the bassoons are slow to activate. For example, on the Bandon register, it happens that we hear the flute (clarinet) before the bassoon.