Methodology
Why different reports include different mantras
How SahiKundli chooses which Beeja mantra each report recommends.
Each SahiKundli report that includes a Beeja mantra grounds it in the astrological principle that report is built on. The planet recommended is the one most relevant to that report's specific focus area.
SahiNow recommends the mantra for your Mahadasha lord: the planet governing your current Vimshottari period. SahiJiva recommends the mantra for your Atmakaraka, the soul significator in Jaimini Jyotish. SahiAnk recommends the mantra for the planet that rules your Mulank. SahiLife: Relationship recommends the Venus mantra, as Venus is the natural karaka for partnership across all charts.
Each mantra is prescribed for that specific report, derived from your chart, for the exact focus area you chose to explore. It belongs to that reading.