As has been said already you are not really understanding the use of the flat depth option when using a Vcarve toolpath. If you hoover your curser over each of the 3 toolpaths you have created you will see that they all cut to exactly the same depth
If you want to carve deeper (using the vcarve toolpath) you would need to use a different font, make the letters deeper or use a bit with a different angle such as a 45 or 30 degree bit.
You are not cutting very deep to start with so if your stock is not perfectly flat & you set your z zero on a high bit of the material & your text is positioned on a lower bit of the material then it will not cut as deep as it should. Is your spoilboard perfectly flat & have you surfaced your material stock ?
I am not familiar with the program you have mentioned so don't know if that has the same sort of vcarve option or just an engraving option where you would set the depth of your engraving. You could try using the engraving option in the vcarve software to see if you get the same results as your other software