You have the possibility to use those params already in place (width, height, etc). See:
Regarding svg and pdf generation, they are out of order for me with latest tiki versions (e.g. Tiki12), I still didn't have time to investigate why and fix it.
But for sure there are many other ways to handle in pure R in your script the output type, so that you could produce svg or pdf by other means in pure R, etc.