If the A descriptor is used without an explicit field-width then the length of the character item in the data-transfer list determines it. This is generally what is required but note that the position of the remaining items in the record will change if the length of the character item is altered.
If is important to use fixed column layouts the form Aw may be preferred: it always uses a field w characters wide. On output if the actual length len is less than w the value is right-justified in the field and preceded by (w-len) blanks; otherwise only the first w characters are output, the rest are ignored. On input if the length len is less than w then the right-most len characters are used, otherwise w characters will be read into the character variable with (len-w) blanks appended.