Basic pixel math for HA addition

[astrodoc71]

Trying to ultimately add  Ha into a red file but first preparing the Ha file. This is the equation I am using but getting a weird result: ((integration_linear_fit_HA_M1_crop_decon_20 * 60) - (integration_linear_fit_red_M1_crop * 14))/ (60 - 14).Not sure what parameters to adjust or perhaps there is a setting I am missing?. My Ha filter is 14nm and my red I believe has a pass band width of 60. The Ha was unbinned and the red file was binned originally
Here are the 3 files: Ha, red and result of applying the math to the Ha file (labeled "pixel math")
These are all links to direct downloads
Ha file: https://www.adrive.com/public/gZqM6Q/integration%20linear%20fit%20HA%20M1%20crop%20decon%2020.fit
Red file: https://www.adrive.com/public/UKUgvn/integration%20linear%20fit%20red%20M1%20crop.fit
Result of applying to the original Ha: https://www.adrive.com/public/uV6VcW/Image04%20pixel%20math.fit
Thanks
Dave