HDB Resale EHG Grant calculation

I'm intending to purchase a resale flat with my partner but we are very confused over the calculation of the EHG grant. My partner (Partner A) has worked continuously for the past year while my (Partner B) last drawn salary was last June. According to the HDB site, they will take your average gross income over a 12 month period, which means they will divide your total income for the past year by 12 to get the average per month right? However, from the Example 2 on the EHG grant page and someone's experience on another forum, they took Partner B's one month salary as the average gross income without dividing it by 12.

Has another been in a similar situation and how was your EHG grant calculated? Do they calculate your average by dividing it according to the no. of months worked rather than 12 months? Would really appreciate your input as this can seriously affect the amount we need to pay in cash. :-(