So many of us brass players automatically tongue a lot harder when we play louder and we don't even realize it. These two things must be separated. In fact, the best professionals are able to separate all aspects of their playing and adjust them independently of each other.
When a conductor asks the low brass to play louder, they have not also asked for it to be heavier, slower, sharp and with a bad sound. We just frequently throw all of those in as a bonus!
I once heard Joe Alessi say that air and tongue can be adjusted like the oil to gas ratio in a mower. He went on to say that playing forte is 90% air and only 10% tongue which I agree with.
I think most of us, from the very beginning, use way more than 10% tongue when we are playing forte. This has to be reprogrammed which takes a lot of intentional practicing over a prolonged period of time.
The proof of course lies in recording yourself. If you hear too much tongue, adjust it. In fact, keep adjusting it until you have gone too far. You have now framed the problem and know that the perfect solution lies somewhere in between where you started and where you ended up. Always let the recorder be the ultimate arbiter.
It's also worth noting that this kind of self-awareness is universal in players who are able to reach the world-class levels that Warren Deck, former Principal Tuba of the New York Philharmonic, reached during his playing career. He wouldn't have gotten to the root of his over-tonguing problem by simply tonguing less on a case-by-case basis. He figured out that he was doing this every time he played louder and so was able to address it on a much more fundamental level (which I'm sure led to a permanent fix with just the occasional exception.)