Dear Suan,

a> upanissaaya - near, in the vicinity." ???

a> The phrase "Saavatthi.m upanissaaya" is best translated as "replying
a> on depending on, or counting on Saavatthi".

a> The phrase "upanissaaya" comes from the verb "upnissayati" (to rely,
a> to depend).

Indeed it is an absolutive.
'Upanissayati' also means 'goes near to', so 'upanissaaya' also has
meanings 'going near to', 'near (+ acc. or gen.)'.

(Please see 'upanissayati' article in Margaret Cone dictionary).

Metta,
Dimitry