when i am testing for n- or n+ development i use 30% increments to get where i need to be..

parhaps 15% isnt enough.

also, theres 1million different ways to develop/agitate film (and rodinal probably accounts for 900,000 of those ways) but ive always found that agitation every 30 seconds is too much no matter what developer/film i used..

at some point my standard became: agitate every minute