I was not working with NSProgressIndicator but I worked a lot with UIProgressView (iOS analog of NSProgressIndicator). And it is impossible to change UIProgressView's height neither in IB neither by changing its frame property.
But there is a nice workaround! In iOS you can use transform property to change the height. Following will reduce height by 50%:
_progressView.transform = CGAffineTransformMakeScale(1.0f, 0.5f);
Maybe you can use the same workaround for NSProgressIndicator.