Hurt less to pin quad when standing

So I tried to pin my left quad this morning while sitting down.... No go. Everytime a dull pain would kick in.

Same thing happened with my right quad a few weeks ago then I stood up and it was fine.

This time though I didn't have time to mess about so I hit the vg instead.

Any reason why this may happen or was it just a coincidence?

Gonna take some getting used to dude.

I can do it either way. Not much difference. But I'm more comfortable while sitting. I like to prop my foot up on something like a foot off the ground so my leg is between bent and straight if that makes sense.