fixing grey/silver hair?

I had a blonde ombré for a while and my natural color is a dirty blonde so when I decided to go silver/grey I thought that I could use wells 050 over my ombré to get grey. But since the darker part of my ombré was a darker blonde, only the lower half of my ombré is grey. I really like the color and I want to get all of my hair grey. I've tried letting the bottom fade out before I bleach the darker hair but I've only been able to get it to a light silvery color. I was thinking I could just lighten the dark blonde upper portion and leave the ends grey and then cover all of my hair with the wella 050 in hopes that it will all end up the same grey but I'm not sure if this is the right way to do this. I don't want to bleach my ends again because before they were grey they were already white blonde and I don't think bleaching over they grey will be a good idea. If I bleach the top then do it all grey will the top and bottom of my hair match? (When I use the wella 050 I just mix it with developer and leave on for 20 minutes)