Are you blocking on the ‘a’ or the ‘p’? If it’s the ‘a’ then you gotta focus on your breath before even worrying about the sound. If you’re not exhaling then the words don’t matter. If it’s the ‘p’ then my assumption is you’re flying through the vowel sound and rushing straight into the brick wall that is a hard consonant like ‘p’. If that’s the case, try and slow down the vowel sound so you can focus on making the next consonant sound more soft so you don’t block as easily. Hope this helps