I am 5'7.5" and 145lbs.
Most people I spar with are around 5'11" and sometimes 6'3" 145lbs.
This usually equates to my opponents able to hit me about a half foot farther away than I can hit them. So what is a shorter person supposed to do?
I flip the game around.
Rather than spar outside where they can hit me with ease. I time their attacks, and get inside. From the clinch, now I am able to hit them a half foot closer than they can hit me.
Transitioning from the outside to the inside requires agility, and timing, it's also a neat way to score a punch getting inside. Once inside, it's like being in a safe zone - your zone. If you know how to control your opponent with underhooks, hip position, and superior balance, you can create openings for your own short distance attacks.
There is always a way to win, and everyone is capable of earning success.
Now if you are actually a Tae Kwon Do sparrer this portion is for you.
There are 3 timings you can get inside, each with their own risks and opportunities
1) Before your opponent attacks.
2) After your opponent attacks.
3) As your opponent attacks.
1) If you go before you opponent attacks, you must be quick and go on the off beat, before your opponent can prepare with a hard counter such as an Ax kick, Back kick, or high section front leg. Setting up your opponent with multiple feints and off rhythm movements will allow you more unpredictability to go in. This will also help with a wary tall opponent who is ready to step back (hoojin) or slideback short range roundhouse kick thereby retaining their long distance.
If you keep on doing this, likely your opponent will start backing up to retain distance or go with hard counters to a forward stepping opponent. This opens up your spin kicks.
2) Going after your opponent attacks assumes that there is a break. This is usually if the opponent drops their leg after an attack and does not re chamber or if they are transitioning between a front leg attack or back leg attack and especially after you block or parry an attack. This window allows enough time for you to step in and jam before the next kick can go off. This is pretty easy to do at amateur and low level sparring, but quite challenging to do if someone is cut kicking - which is the current meta of sparring. For this reason rather than try to go inside after a cut kick, it is better to off balance your opponent by variety of cut kick cancels than take the risk, or to block the attack and then go in.
If you keep stepping inside after an attack, a savvy opponent will prepare a slideback counter after their attacks to tag you going inside.
3) Finally going in as your opponent attacks at distance. If they are coming in aggressively you can block the kick and simply stand your ground to get inside. You can also step in aggressively as soon as you see them coming forward to essentially get inside before they get chambered for their kick.
If you keep on doing this, a savvy opponent will look for hard counters, like ax kick, back kick or start to feint you to bait the inside and then counter the instep.
Basically there are plenty of opportunities to come inside, but any one timing used will give you opponent an opportunity to easily counter. So mix up your timings.
The game changes when it becomes electronic scoring. When a simple flick or light side kick can score a point, a taller person is more inclined to keep a cut kick ready. This way you need to address the cut kick before coming inside, which is where the game currently is. Now a shorter fighter must play a cut kick neutralizing game in order to then get to the next step of inside. Think of it as another boundary to conquer, and whole other topic to discuss.
Until then, fear not my short leggers, there is hope.