Resizing parameter box in RooFit

Roofit and RooStats
1

Hello

Is there a simple way to resize the parameter box produced with RooAbsPdf::paramOn(…) ?
In my macro I make:
pdf->paramOn(myframe,Layout(0.65,0.95,0.95));
but this allows me to set the position of top of box (ymax), not of the bottom - which is calculated automaticaly - and I also would like to set the bottom position by hand (in order to stretch the text).
Is there a way to resize the TPad?

Thanks,

Timothée