Zbrush alpha falloff ?

Digipyro

Hey guys, I'm just wondering if there's a way to fix the falloff from Alpha's in Zbrush ?
Whenever I make a black and white image in which black is suposed to substract and white should stay constant 
it still raises an area around the black parts.

I've been trying it with the inflate brush, on drag direct and makes my Straight shape all messed up ( see image)  Tried masking it too but same problem persists.  The alpha is black and white with no alpha channel ( did add this at one point but didn't seem to do much), I tried the RF value but this just fixes the straight edges on the border tried the other values in modify alpha too.
Edge on top and bottom should be straight as before I placed it.

Ghogiel

Using a mid grey instead of white would be the proper way to set up that alpha. There is a mid value slider in the alpha options though that might help correct that issue.

But for the edge and bottom being affected, Not sure how masking isn't the solution to stopping edges being affected by a brush .

Digipyro

I tried masking the edges but then you get a hard edge at where the mask is =<. I'll try the mid value slider / grey though. Will let you know if this was the solution.