@mmcdara Thank you. However, your claim is not true, in several ways.
For regular output, the following can be done (since about Maple 18 or whenever 2D plots got the size option):
The difference is that the code in the Post (at top) enables the size option to be used directly in each plotting command. That's more direct than modifying a generated 3D plot result, after generation, with such a Resize procedure. That is the central idea of this current post.
Since you mention DocumentTools, well, there too it is possible to embed a plot that is either smaller or larger than default. Your code snippet is just not one of the ways to enlarge it. The DocumentTools facilities also allow for embedding of programmatically scaled and panned plots. But note that these DocumentTools mechanisms are only for embedded display effects, whereas the size option produces a plot as output/return-value and which carries its size details as part of its structure.