Hi Kevin
I am hardly an expert on Howatt bows – but believe the brace height should be in the 7.5 – 8″ range. It is my understanding that the factory still makes some of the Howatt bows and they are sold thru Martin Archery, you might give them a call. I personally always try to find out the bowyers / factory recommendation for brace height and stay within it – less chance of future problems — . As you know, twisting the string in and out is done to adjust brace height. Since you are only getting 6.25 with the string you have, I am wondering if it is the right string ( too old / worn /)? Martin might have, or recommend where to purchase the proper size/type string for their bow.
A Howatt collector on another site had a number for the (Howatt) factory – 509 248 6900 – might be worth a try.
Scout