me and this damn sweater

I've probably posted about a thousand times about the "Incredible, Custom-fit Raglan Sweater". I debated about doing it for a long time, and a few weeks ago I bit the bullet and started it. Well, long story short, I got 3/4 of the way done and ripped the whole thing out. I made a lot of mistakes, I know what I did wrong, and I started again.
Now I am at the point of one of my mistakes that I'm just not sure of. The sleeve.

It says "Decrease one stitch at the beginning and end of the round every inch or so".
The last one I made the sleeve was huge (diameter wise). Is 2 stitches an inch really enough? My gauge is slightly different this time, was 4 stitches an inch, now 3.5. So this decease will be a little more than half and inch decrease in width for every inch in length. I really don't want to make the same mistake twice and have it too wide, but also don't want to decrease too often or more stitches and wind up too narrow.

Any advice???