That is DIMEXO system variable. The default is 1/2 the text and arrow size.
Manual drafting days it was kept between 1/32" and 1/16", basically clearly not touching the object, but close enough to be clear where it's going.
Wow how long was the blue string. Kidding there is probably a drafting standard somewhere, using lisp usually a factor of text height. Say 2 x txtht or 3 its about readability.
Your image has a large dimension gap maybe make that a bit smaller 1st. Personal preferance.
The 8' and 8" look like a good spacing. 2xht ?