PSA: as the front line, you should always be in front for your backline
In any situation, as the tank you always want to be in front of your carries to block skillshot and cc.
An ahri flash charm? Eat it. A blitz hook? Take it. It's better for you to get cc than your carries to get cc. You have a chance to survive and still contribute to the team when you got hit by the skillshots, your carries probably don't.
Especially in sieging situation, whether you are sieging or getting sieged, you need to stand in front of your carry so they can safely hit the tower/wave clear without worrying about getting hit by enemy hard cc or taking a shit chunk of damage.
for example, a
team is getting sieged on,
can kill the wave with two w, but enemy has a
who can hook velkoz when he stands forward for waveclear. Now as the tank what should you do? you stand in front of
so he can wave clear and enemy can't get damage onto the tower. If you get hook by blitz into his team then congratulation that is basically what 90% of the tanks wish for every day.
TL;DR Always stand in front of your backline when you are the front line and body block for them. You might feel like it puts you in a dangerous position, but it is better than your carry being in one.