It's not overhead. The dog days start with the heliacal rising of Sirius (i.e., when it rises in the east just before the Sun). Canis Major is nowhere near the elliptic. The dog days run from early July to around the second week in August. I explained this a couple of weeks ago. I can't remember which thread now. Unlike you, I looked it up first.

The temperature here reached 32.2°C here today. We've been here for 35 years and today was the second-hottest in all that time. The hottest (and hottest ever recorded for Devon and Cornwall) was a mere three weeks ago when we reached 36.0°C. In the last month we've had five days above 30°, which is ridiculously unprecedented round here.

Sounds feeble compared to Maggie's reports, I know!