are you trying to tell me that DHL sometimes go through customs and sometimes not ? sorry i don't buy that... DHL is a corporation and corporations use well defined processes for every action... i bet my bottom dollar they handle all packages the same way.
Everything goes through customs, but customs can not check each item. Therefore if you are lucky you don't have to pay anything even if the value is above the tax threshold.
i don't know how German customs work, but over here EVERYTHING goes through customs and it's the post or transport/parcel company who asks to release the packages with indicated value below 22Eur. if the indicated value is above 22Eur or the customs officer doesn't believe the indicated value under 22eur (e.g. package too big or heavy), then it has to go through the process and you have to fill in the "common customs declaration" form (the how-to for filling in that form has approx 70 pages), get your EORI registration, provide proof of the actual price (invoice, bank statement) and spend few hours at the customs office, then pay the VAT + customs fee they calculate and the package is released.
if you don't want to handle that customs process, then you simply let the parcel company do it for you. over here DHL does it for 2% of the customs duty/fees , 18Eur minimum but 90Eur max. for me it's much cheaper to let DHL do it because i can make more than 20Euros during that time spent filling the forms and time spent at the customs office.
and of course even if the order is below 22eur and you don't pay VAT+customs you still pay the 18Euros to DHL for handling it. that's why to use postal service for orders below 22Eur they will handle customs for free (request releasing the package by the customs because it's under 22Eur).