Why does my dick look big when I'm laying down, but short when I'm standing?

7.5 x 5.75. 6.5 nbp.

I'm 6'1 and 170lbs, so kinda lean for my height. I would expect this to help it look big when I'm standing, but it just doesn't.

It's not the end of the world, but I really wish it looked bigger, and I'm not sure what's going on there.

What's weird is that it looks huge when I'm like 50% hard and not pointing upward, but when I get harder, it starts to look smaller even though it's grown like an inch or maybe even more.