Hypothetical top-down knit hat pattern

After the first hat I made for Baby N turned out way too small, and then repeatedly starting (and frogging) a second hat because it was either too small or too big, I decided that top-down was the way to go, because you can fit it as you knit it. It was difficult to choose a pattern, though, because naturally I must consider all patterns available either online or in library books to determine the very best one--which I was ultimately unable to do. So I made one up using bits and pieces from several different sources.

This is for a simple cap in stockinette stitch with half an inch of 1x1 ribbing.
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Cast on 6 sts using the figure 8 (aka wrap) method. *K1, M1* all the way around (12 sts). (For this purpose, M1 = knit in the back of the loop then the front of the same loop.)

Rnd 2: K.
Rnd 3: Increase 6 sts evenly spaced.

Repeat rnds 2 and 3 until the circumference looks almost big enough.

Now do the following calculation:
1. using what you've knit to this point, determine your gauge, G sts/inch;
2. measure the wearer's head circumference, H inches; and
3. the number of sts needed for the circumference, C = 90% x H x G.

Continue repeating rnds 2 and 3 until you have C sts.

Now, measure from eyebrows to the base of the head, L. The length of the hat (from cast-on to cast-off edge) should, in theory, equal 1/2 x L.

Knit straight (no increases) in stockinette st, until the piece measures (1/2 x L) - 1/2 inch.

Switch to knitting needles that are 1 size smaller, and knit 1/2 inch of 1x1 ribbing (K1, P1).

Cast off tubularly.
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So, that is the hypothetical pattern. Now I just have to test whether it works.