Round Duct drop/rise symbols

[loujr]

I'm using MEP 2013 and I am trying to adjust return and exhaust duct to show a single slash for drops and rises rather than the "x" as in supply.  I know how to create the block and assign it to the Duct/Rise symbol but I'm having a problem scaling it to fit inside the cirlce rather than extend to the size of the square equivalent.  For example, I insert a 6" round Elbow up and when I use the "standard" drop/rise symbol it inserts an "x" inside the circle.  When I use my custom drop/rise selection (which is a single slash) it inserts it as if it is a 6x6 elbow down not a 6" round elbow.  Why does it do this?   I had no problem customizing the rectangular symbols.