Letter Spacing in PX

Is this being looked at? am finding it a headache to work out the correct numbers so that the development team can be accurate:

I have a Header text at 61px with AV set to 16.4. In code this equates to -1px in the code which is what I want.

Then I created a larger header size at 80px but 16.4 AV = -1.31px in code;

I now have to spend time with trial and error to get my larger text size to -1px

To make XD more successful it needs to be a tool that can be used across all team disciplines. and be design for digital