for the decrease there are multiple options.
I guess, my first increases would "eat up" the places between the cables... just decrease on either side of the cable bands. How many rows you do inbetween the decreases, I would eyeball.
When you have eaten up all stitches but maybe one purl between the cable bands, your hat will still be too big of an opening on the top.
Then you can eat up one knit stitch in every cable string / rib, so that the cables themselves become narrower.
In the very end you will probably not cable anymore but just run the st st ribs into the middle. There you can finally just decrease by k2tog or the like.
I made a hat this spring that decreases between (much smaller) cable bands.
But if you like the shape, maybe take the increase rate from my pattern(free pattern, of course)
Importent is: how many stitches to lose on how many rows.
if you decrease 4 stitches every round, you get the same decrease rate with 8 stitches every 2nd round... just as an example. Of course the fit will slightly vary due to the increase stepping.
How many bands of cables will you run up the hat? do you know yet?