with short row heels, you don't make a flap!
you start (row 1) of the heel, with Knit X (where X is 1 less total) wrap and turn,
Purl X-2, wrap and turn,
Knit X-3, wrap and turn
Purl X-4, wrap and turn
Knit 29 (of 30 stitches), wrap & turn
Purl 28, wrap and turn,
Knit 27, wrap and turn
Purl 26, w&t.. and so on, till you have about 1/3-1 or 2 stitches left
so if you start with 60,(sock) and work heel on 30, you decrease till you have 10 (1/3 of 30) and then do 1 or 2 more decrease (8 or 9 stitches) at which point you begin to 'pick up the wraps' (increasing 1 stitch per row) till you once again have 30 stitches.
(for different numbers of total stitches, you'll have different number of stitches at 'end of heel shaping)
(72 total, 36, heel, 1/3 of 36=12, 1 or 2 less, 10 stitches--and then start to pick up wrapped stitches--
for 56 stitches to start, 28 for heel, 1/3 of 28=9.33, minus 1 more, makes it 8 stitches before you start to pick up wraps)
if you have worked a flap, and need to turn a heel (also done with short rows, there are other 'formulas's for turning heels (and several styles--round, v, half round, square, welsh) and each has a different formula!)
round is the most common, square is the easiest! you can google round heel and find several sites that have charts with all the numbers 'plugged' in.