@Picture_Frames_UK_LT it sounds like you will end up sending all the awkward shape parcels with DPD if too big for Amazon Shipping. DPD like small parcels, as most hubs are automated they need to keep the mix between large and standard size parcels small. Our contract with DPD allows approx. 15% over size (more than 60cm but less than 1.2m). We just have to be careful with sizes and have re-designed several of our products to fit within the Amazon Shipping size guidelines.
If you struggle with DPD maybe try Yodel as they are an approved carrier and we use them for out of area or when the shipping site shows ‘misses expected delivery’.