Custom brushes for grease pencil

Hey there

I made some custom brushes for grease pencil and so far they work pretty well 

and I hope I can soon make them puplic I only have two problems

1. they are not getting bigger then 500 px and that's abit annyoing when you want to add a nice water color effect or just any for a lager scale. 

I tried to make my png bigger that I used for the texture but nothing changes and they stay small

is there a way to fix this- other than making my scene smaller

2. When I try to draw on a layer that already has been created with older brushes - as soon as I want to draw a stroke with a new brush it deletey the old ones. layers are not locked and I use the recent Blender

when I make a new layer all brushes work fine >.>

https://www.dropbox.com/s/37i54316o5k25cm/hwatzthe.gif?dl=0

any ideas on that ?