Meaning of red blood cell volume expansion
Red blood cell volume is the percent of blood taken up by red blood cells (also known as the hematocrit), and is expressed as a percentage (so, normally, RBCs should comprise x% of blood by volume.) It says nothing of the size of the red blood cells. 

That needs to be done by measuring the mean corpustular volume either by special machine or by looking at a slide of cells. So if the MCV is not mentioned, you can assume that expansion is referring to increased number of RBCs.

Smaller than normal RBC's are called microcytes, larger than normal are called macrocytes. 

Recombinant EPO just increases the production of RBCs (and, unfortunately, it has some other effects as well.) It should not affect the size of the final erythrocyte.