IMagick is a native PHP extension to create and modify images using the ImageMagick API. ImageMagick Studio LLC did not write nor does it maintain the IMagick extension, however, IMagick users are welcome to discuss the extension here.
All I can say is what the php documentation says; where did you get ImagickDraw::setStrokeType() from?
When I use stroke it has been on the outside as standard - how would getting it on the inside work. Do you have an example of what you want; something drawn in another program would be useful.