There is no 1:1 when converting to scopes, 1:1 is only possible if the FOV is the same. For scopes you have to match a specific aspect of the sensitivity, be it tracking speed (MDV 0%), flick distance (MD X%) or 360 distance.
If you just change the settings in MW and not the conversion setup, nothing changes in the calculation for the output game, you are just changing how sensitivity is calculated for MW.
If you change MW to relative and 1.33 you also need to set the conversion for ADS and Scope for MDV 133%:
https://www.mouse-sensitivity.com/?share=50cfa04fdfb857a843abddff9f05aa9f
You need an even lower DPI, the range in Dead by Daylight is very limited. If you select Hipfire instead of All you will get a maximum DPI suggestion (does not always work perfectly depending on the conversion).
If you share a link to your conversion I can take a look.
Ok, the issue is that when going from 400 DPI to 1600 DPI with that setup you will (as the red text implies) need a sensitivity of -2.5 (but the minimum in-game is 0).
So the only solution to this is to switch to config file sensitivity which has a wider sensitivity range: https://www.mouse-sensitivity.com/?share=c6dabab3d679fde27e0e008e68679f48