To hold the uniform width/depth of cut will come with just more practice. Yes, at first dive in steeper and then level out to hold a width.
The size of chip that you're trying to throw out at the end looks pretty big... and would be tough to throw. And if you did end the cut at that depth by throwing the chip, it wouldn't be the best looking. If I can get out of it, I generally try not to end a single cut at that depth abruptly because it is hard to make it look good. However, a way to do this easier is to take several light cuts to get to the depth/width desired.
There were two wide cuts that ended similar on Straubinger flute logo (S), however there was a fine line at the end that I could use to end at. If this cross was not there I would of still used a fine line but not extended it past the size of the wide cut. Does that make sense? Below is the S from the logo. The cut was at the two ends of the S. Place the fine line in first and then come up to it with the wide cut and throw the chip, or leave the chip and go back over your fine line to cut if off.
I was never very happy using a flat graver to make wide cuts with. (too wavy and the inside edge not very clean). With the wide bright cuts in the flutes and also the lettering I was using around a 123 - 124 width. With these kind of example cuts, you may want to try grinding a wider V and see if you like that better for the wider cuts. A wider graver can help end a wider cut easier too, since the cut is more wide than deep.
To make those wide cuts you did with a flat that are wavy and even the ones with the wide V look better, make a small V cut on the outside of the flare. It can true up the uneven parts, plus gives a little extra nice touch look.
I have to say, your cutting looks very advanced for just starting out.
