Fiberboard equivalent to Hardiboard or Durock?

After old floor tearup, I learned that I actuallly had 1/4" less height to bottom of existing toilet flange than first thought. So, I changed original plans from adding 3/4" ply over 1/2” subfloor and installed 5/8"BC ply instead. Toilet flange is not level (about 3/32" lower in front than back). At the front side I now have a very light 1/2" space to the underside of the flange. I have not yet shopped for tile, but assume 1/4 thickness is common, I plan to using 1/4” backerboard.

Saw 1/4" Fiberboard® backerboard at Home Depot, is this an equivalent product to Hardibacker or Durock products? Or do you not recommend for my job. Does Durock come in ¼” thickness?

Since flange is lower in front, Should I force the backerboard and tile under the front side of the flange? Both flange and waste stack are made of black plastic and the stack offers no verticle moverment.

THanks for all the great advise so far. Great forum!

It's a Hardi knockoff.

Fiberboard is a Hardi knock off produced by USG. What is funny about that is for years USG told everyone that Hardi was junk now they make a product that is "like" Hardi but it really is not - made out of recy newspaper and dipped in some type of sealer. In my eyes Permabase would be the best then Durock or Hardi and then fiberock as a last resort. - Martin