Georgiee, firstly, I'm not a runner. Also type 1. I'd bad low bloods. On a hike late Sunday.
Air temperature- HEAT might cause us trouble, I think we need less quick acting insulin in heat?
Are you able to reduce the overnight insulin a little, after running a 10k? You didn't have lows during the run? I'd say you're on a quick acting and a background insulin.
I reduce my background insulin by 2 units before a steep hike. It still brings down my bloods 6 hours later. I reduce my lunchtime insulin/eat extra carbs at lunch. Last Sunday I didn't factor in the heat on the mountain, I'd presumed there'd be a cool breeze.
Do you eat beans, eggs? Breakfast of normal tinned baked beans and an egg help me keep bloods stable on a hike...and I didn't eat them last Sunday...