The head wasn’t a lot smaller. His helmet was tighter to his head in TFA than the original sculpt made it out to be.
The GA helmet had a smaller chin strap than the Strike helmet, but was very well proportioned to what was on screen.
The head IS a lot smaller. Just look at your picture and compare the GA cap head to the two Caps to your right.
Hot Toys blew it big time with the stock head.
A lot of people thought that the body was too bulky in comparison with the proto, but the issue is that the proto had a bigger head so
it was proportionate to the body, but when it went to production, the head shrunk.
That's why when people started to replace the head with the bigger Steve Rogers head, the body didn't look bulky anymore and looked
more proportionate.
When I compared the GA head to the TFA head, the GA cap's head was actually smaller than the TFA, which is already on the small side.
The issue with the stock GA cap is shrunken head and the skinny jeans.
When you look closely at the proto, the head is bigger and pants are looser.
So, replace the head with a bigger sculpt, wet the pants and yank them all over to loosen it up.
And as a cherry on top since this is my favorite Cap figure, I gave him the CW shield.
And the figure is a lot more like the proto. I'm partial to this suit, so its actually my favorite Cap figure.