That's probably for the best. Lance would have started at the bottom like an idiot and probably compromised the integrity of the beam. Starting at the top makes way more sense. Maybe he should do the bottom and meet in the middle? But it's hard to think when he feels like he's about to vibrate out of his skin and turn into a nuclear bomb at any moment. Shiro's response jerks him out of those thoughts.

"Oh. Yeah. It's totally normal." It's said in a distracted tone, but then he pauses and rethinks, "Well actually, it does feel super different this time. I dunno what the deal is."