The 1/8 would be cut at 3/8 .... what I had done with making the bias for my Celtic block ... was to cut a strip from card stock or 3x5 card at 3/8 and placed in the middle of the 3/8 cut and iron each side to the center. Making the 1/8 bias....
I am not sure what to tell you for the 3/16.... 5/16 and do the same I am guessing.
I used the mini iron by Clover to press my bias. Used a small ironing mat and sat and ironed away. I cut my bias from fat quarters/ you get quite a bit from one.
You may find it easier to work with short pieces than a really long one. Hide your starts and stops at a point where it is covered by an overpass or under another bias piece. I hope that makes sense.