kŕşņāşțami means that the Sun is ahead by 8*12 to 7*12 degrees, approximately.
ie., ( 96 to 84 degrees ) * 27/360 nakşatrāņi ahead
ie.,( 8 to 7 ) * 27/30 or 7.2 to 6.3 nakşatrāņi ahead.
and 84 to 96 degrees or 6.3 to 7.2 nakşatrāņi ahead of the pūrņima (full moon) nakşatram.
We count six forward from röhiņi to makhā and seven to pūrvaphālguņi, for the sun’s position.
And we count six backwards from röhiņi to pūrvabhādrapada and seven to śatabhişa for the nakşatram of the full moon.
In śrāvaņa māsē we expect the full moon near śravaņa nakşatram or close to it. This time it was two nakşatrē ahead in śatabhişa. ( I think that if it occured in pūrvabhādrapada it would have been bhādrapada māsam. So I’m going with śatabhişa).
So the position of the sun at the time is śrī kŕşņa’s birth was pūrvaphālguņi as per my present level of understanding.
(Today we have kētu in śatabhişa and rāhu in pūrvaphālguņi).