You may have found too much in the way but mount inside cupholder or else the table above vents is likely sturdier than vent. This high power wireless charger might possibly fit though I haven't installed in EQC, only on other's cars:
Or just behind the cupholder you could put neater different one such as listed in this thread:
www.mbeqclub.com

Auckly 15W Fast Qi Wireless Car Charger [Electromagnetic Sense] Car Wireless Charger Automatic Phone Suction Holder Dashboard Mount Compatible for S21/S22,for iPhone 11/12/13/14 Pro Max Mini Plus etc: Amazon.co.uk: Electronics & Photo
Auckly 15W Fast Qi Wireless Car Charger [Electromagnetic Sense] Car Wireless Charger Automatic Phone Suction Holder Dashboard Mount Compatible for S21/S22,for iPhone 11/12/13/14 Pro Max Mini Plus etc: Amazon.co.uk: Electronics & Photo
www.amazon.co.uk
Or just behind the cupholder you could put neater different one such as listed in this thread:

Wireless Phone Charging
Hi, just getting used to my new EQC. There are a few things I was expecting to find in my vehicle that aren't actually there. One is wireless phone charging. This is shown as included in all the marketing material on the Mercedes UK website and my Merc dealer in London even confirmed it to me...