The image "Rangefinder round the Church" from my gallery was developed with 4 ml of Rodinal in 1,200 ml distilled water for 28min @ 20° C / 68 °F... I used only 400ml from those 1,200ml.
Agitation is a very important factor, especially with Adox CMS20! In my experience 1:50 might work if the scenes You shot were of very very low contrast. If You could "sacrifice" the 1st few frames form the roll, just cut them in the dark room and try them out in 1:50..