@richardpowell.powell so this how I do it using t-splines. You have to remember that I save these fonts for reuse. I also do mainly high end pieces so for low end stuff the time might not warrant the effort. This letter is 2.8mm high and .3mm deep and I have successfully cast it in the past
Create your curve and extrude to the depth you want.
Then you angle the walls to your preference and close in the bottom nice and smooth. To finish off go back to the top and extrude horizontally to give you a nice round top edge. Helps if you know t-splines here.
Make a copy of your t-spline in case you need to make adjustments or for reuse. Convert to nurbs and trim it into your surface.
Out at a more realistic view the letter still looks sharp.
Up close nice and smooth for renders, assist metal flow and minimise the risk of investment damage during casting.
HTH.