You have a number of issues with your drawing that lead me to believe you are a relatively new user or haven't been formally trained in how to use AutoCAD. I will discuss best practices first:
1. Use mleaders rather than qleaders/leaders. This generally works better. They slightly buggy when being stretched but otherwise they are far superior to qleaders.
2. Use fewer dimension styles and keep them consistently defined between drawings. In the main drawing, for example, you have defined the arrowhead size at 9" but in the block-1 drawing, it is 6". Elements controlled by styles are controlled by styles in the host drawing and those styles don't change when another drawing with the same style names are inserted.
3. With CAD, always, always, always specify the paper sizes of dimension elements. Either use annotative scaling or use the dimscale setting to scale dimension elements to model size. Never specify sizes of dimension elements in model size.
4. Always use 0 height sizes for text styles. Using any other height will introduce confusion, especially when those text styles are used in dimension styles.
5. Avoid pasteasblock, especially when pasting a block. It creates anonymous block names which are meaningless. You are labelling blocks in the host drawing as "block" but in reality, they each have a different block name and different contents even though they look the same.
6. Avoid block names that are meaningless.
Now to your questions.
- Arrowhead size: a. THIS ARROW HEAD IS SUPPOSED TO BE 12". b. THIS ARROW HEAD IS DRAWN AT 6" IN THE THE DRAWING IT WAS CREATED IN IT IS NOW CHANGED WITHIN THE BLOCK.
- The arrow size specified in ARROW dimstyle in block-1 is 6". The ARROW dimstyle in the host drawing defines the arrow size as 9". Style based elements are redrawn when being inserted to conform to the current style. That is why you should always use a template with basic style information. 2 x 9" = 18".
- Dim style: NOTE: THE LINEAR DIMENSIONS BEHAVE CORRECTLY (When comparing the size of text in a block scaled 2 and dimensions in model space.
- I don't understand how the two dimension text sizes aren't different sizes. The one in the block inserted with a scale factor of 2 should be twice as big. There are problems though. Tick dimstyle defines the text height as 12", but it is 15" in the dimension object because the text style has a fixed height size of 15", which overrules the dimstyle setting.
In short, the drawing is completely botched. To solve, start again with paper space sized dimension styles with either annotative or fixed sized scaling. Avoid using text heights with fixed text sizes but if used, never use them in dimension styles. Stop using pasteasblock. Don't scale blocks that should be the same size differently in a single model space.
Architect, Registered NC, VA, SC, & GA.