The acronym begins with the letter "A" standing for "Angular".
The sound of this letter "A" in ASET can be kept the same as when you begin to say the full word "Angular". This then logically leads to pronouncing the entire acronym as "asset".
Looking acronyms up in up in Wikipedia one finds a true mix of pronunciations which seem to follow no exact set of rules.
It is mostly a matter of which way an acronym is easiest to pronounce based on the exact set of letters and the style used by the organization which uses it frequently.
It is much like some regional speakers would say "A child: using the long vowel sound of "ay" and in other regions it would be said using the short vowel sound more like "uh".