DLM is dynamic, you have a 10day training period after a port reset when DLM tires to give you the most stable line with out sacrificing too much on speed. in that 10 days you may see a couple of resyncs and changes in speed. this generally lowers your ping and sometimes lowers your bandwidth. after the 10 days thats normally the DLM profile/sync speed you are stuck on. I havent seen many people go up in sync speeds after the 10 day peroid, the only exception is if they go from a 8B band plan to a 17A band plan, which as pointed out earlier requires those 3 factors.
you havent posted up your INP or delay stats so we dont know what DLM profile you are on so we cant really give you too much more info on how your line will end up.
FYI, i lost 17A about 2.5 months ago due to a line fault, i started back on 53Mbps then dropped to 52Mbps but gained about 16ms less ping.
The fact that more people are hopping on VDSL because they cant get fiber means those with high sync speeds start loosing those speeds and those with low speeds loose those speeds too.
there is nothing really you can do if the wiring in your house is up to scratch. it is what it is and thats a best effort service.