Using Sum(Case) with Condition

[snufse]

Have following:

sum(case when convert(varchar(10),i.date, 112) >= convert(varchar(10), @DateFromCurrMonth, 112) and convert(varchar(10), i.date, 112) < convert(varchar(10), @DateToCurrMonth, 112)
                  then cast(i.net as decimal(15, 2))
                  else 0
                end) as netqtythismonth,

Now I need to expand as follows:

If date criteria is met (being within from / to date) need to do additional check and operation:

if i.mode = 'J' and p.petroEXcode = 'Y2'THEN convert(decimal(15,2),i.net) ELSE convert(decimal(15,2),i.net) * 42 END) as netqtythismonth

Not sure how to code this. Thank you.