वेदान्त पारिजात सौरभ (भगवद् निम्बार्काचार्य - द्वैताद्वैत वेदान्त ब्रह्मसूत्र भाष्य सटीक)

790 VEDĀNTA-PĀRIJĀTA-SAURABHA [SŪ. 4. 1. 7.
ADH. 5.]
so on, should be super-imposed) on the limb (of the Lord), on account
of appropriateness". That is, the Lord is to be contemplated on as
producing the sun from His eyes and so on.¹
Adhikarana 5: The section entitled "Sitting".
(Sūtras 7-11)
SŪTRA 7
"SITTING, ON ACCOUNT OF POSSIBILITY."
Vedānta-pārijāta-saurabha
One should practise meditation "sitting" only, since meditation
is possible only on the part of one who is sitting.
Vedānta-kaustubha
It has been proved above that meditation, the special cause of a
direct vision of Brahman, is to be repeated more than once. Now,
the problem is being considered as to whether it is to be practised
somehow without following any restrictive rule, or only in a sitting
posture.
On the doubt, viz. whether there is no restrictive rule how medita-
tion is to be practised,—whether in a sitting posture, as lying down,
walking or standing still; or whether there is a restrictive rule that it is
to be practised in a sitting posture alone,—if the prima facie view
be that there being no cause for such a restriction, there is no restric-
tion,—
We reply: "sitting". Why? "On account of possibility,"
i.e. because meditation is possible on the part of a devotee who is
sitting. One who is lying down may fall asleep, while one who is
walking or standing still may have his attention diverted owing to
his effort for holding the body up and so on, and as such no meditation
is possible on their part.
¹ G.B. 4.1.6, p. 9, Chap. 4.