the problem is that I always have the USER_DATA.TEXT_LOB filled, even if the message's size is less than 4000 bytes. I assume to have USER_DATA.TEXT_VC filled in case of short string message (<4000 bytes).
the AQ DB has multibyte character set utf8, so it's about 4 bytes/symbol (and takes some additional overhead per conversion).
By force of experiments i found that message is placed in the TEXT_VC field if its length =<500 symbols.
so i suppose the TEXT_LEN field isn't calculated correctly (as i see it is calculated as per 1 byte encoding). could somebody advice why?