As
@morpheuspapaverus said already it's about tolerance. If I give my girlfriend just 60mg dihydrocodeine she will be straight up nodding. If I take 240mg I might get a mild warmth and hopefully pain relief.
I used to nod off 60mg DHC too, in fact I had a script of 60mg four times a day a few years ago and nodded out for a straight week, but then tolerance happened and with opiates it happens quick. Yesterday I took 80mg oxy + 330mg DHC + 2mg clonazepam + 1mg alprazolam + 20mg diazepam throughout the day, felt a mild high, went into work like normal, didn't even nod. Although tbf I was also on 40mg dex.
(For HR purposes I have to stress I am giving those doses to show how high my tolerance is and therefore how high opiate tolerance can get, and this being the reason why opiate tolerant individuals get nothing from normal doses especially of weak opiates like codeine. If you have low opiate tolerance or are opiate naive, dose like my girlfriend not like me. 80mg oxy especially mixed with other drugs can easily be dangerous for those with low tolerance.)
Ironically though I can still feel codeine even when I'm used to boshing oxy. Back when I could easily get codeine linctus oral solution 15mg/5ml all the time I drank a quarter of a bottle at the same time as dosing oxy and could definitely feel the nice extra warmth from the codeine. I get the same effect from DHC nowadays. Oxy is one of those drugs I find is potent but lacks warmth. I believe this is because oxy is metabolised from thebaine while codeine and DHC metabolise into morphine or related substances. Two very different opiate alkaloids. The thebaine is more buzzy, which is why oxy is the same, while morphine is clean and warm, which is why codeine is the same assuming you have low enough tolerance to feel it.
Problem with codeine in particular though is it does have a dose ceiling and redosing isn't as effective as the initial dose. People always throw around 300-400mg for the ceiling but it varies a lot by individual. There is definitely a point where taking more codeine is just a waste though. This is one of the many good things about DHC, no ceiling.
When it comes to tramadol the opposite is true. Small redoses, even just 50mg, feel the same as taking your initial dose again. But it's so easy to have a seizure on that crap even if you stay below the "safe limit" of 400mg. Fuck tramadol imo. Even after a tolerance break I get nothing from it anymore. Except seizure risk.