All good answers so far!
I found for my self, having shorter legs, I really try to get closer to my target by stepping in and out on an angle (this seems obvious but worth mentioning). If you step straight in you're more likely to get countered and your kick will be "shallow". Stepping out to the left (assuming you're orthodox) while advancing keeps you safer and opens your hips which will allow for a longer reach on your kic. This is assuming you're kicking correctly and rotating your hips etc.