My method of calculation currently is to manually insert a...

My method of calculation currently is to manually insert a premium on the options ( $0.007 in this case across the whole data set, but using volatility 40% and rate 4.74% ). If I remove the manual adjustment ( 0.007 ) and apply the figures you provided ( volatility 100% and rate 1.5% ) I actually get a similar result ( in terms of bags on options ).

For previous example, bags on options with heads at $0.12 was 6.94 versus 6.15 for the chart below. This is the result using volatility 100% and rate 1.5%, but with manual premium adjustment removed. Outcome is quite similar.