brands autoattacks not setting procs off when summoner spell used

Now I may be confused with brands mechanics but it states brands auto attacks will set target. Ablaze for 4 secs. When used with 1 of 4 summoned spells each will react and set off a different proc depends on spell used the issue in seeing is I use a auto attack to get ablaze up then follow up with conflag to set the targets surrounding my main target ablaze ...when i do this nothing happens, but if use pillar of flame then follow up with conflagrate the proc kicks doing as it states rather then when used with the auto attacks..like I said I may be confused on these mechanics, buy shouldn't the procs work with any autoattack rather than with a sequence of summoned spells .