I'm going through this process too, but in the opposite direction. Note that the recommendation to measure your 'shoulder width' and add 2 cm is based on measuring from the mid-ac joint. There are three bony protuberances on the shoulder: the end of the clavicle, the prominence of the acromion, and the outer corner of the humerous (often buried in the deltoid, and lower than the other two. If you're measuring from the acromion, you're effectively already adding about a cm to each side. You want to measure from the divot between the clavicle end and the acromion to the opposite divot, at least as I understand the fit proceedure.

One thing you might do (if you have a trainer) is set the bike up facing a mirror, ride for a few minutes to get in a good rhythm, and look at how vertical your arms sit (assuming your elbows are in a line between shoulder and wrist). When I do this test, I can see how my arms flair out, which confirms my measurements that my bars are too wide. If it looks like you tend to tuck your elbows in, that might be why your hands feel too close together, since that's going to make it less comfortable to breath.