It will be very difficult to control it.
I hate using images as you never know how they will come out - this is just another great example of "Qlik Sense responsive design"
back to the topic - what you can do is to play with actual page size. Imagine that you are printing it on paper of the A4 size, can you change size of your report to be A3?
also provide little bit more info, what template are you using PPT, XLS, PixelPerfect?
did you change default image sizing options - i tend to leave it on a default value as it is more predictable then and i always try to adjust "paper" size so my image can fit on it.
second last comment - as this is an image it is renderred based on some screen resolution - i think it is a NPrinitng engine screen resolution - as you know with QlikSense you can zoom in and out and get completly different looking objects.
last comment - any chance you can build this table using pixel perfect or XLS pivot table instead?