Difference between mid zone ko and flat zone ko?

And which do I run on my linebackers (I run 6-1)

Midzone: 

Defenders with this ability force more catch knockouts and react quicker in any mid-field zone coverage, less than 20 yards from the LoS inside the numbers and 10-20 outside.

FlatZone:

Defenders with this ability force more catch knockouts and react quicker in any flat zone coverage, less than 10 yards from the LoS and outside the hash marks.

Depends on where you set the coverage. 10-20 yards off los mid zone, anything under 10 yards flat zone.

technically, mid-zone covers more ground while flat zone is restricted to outside the hash marks and less than 10 yards from the LOS.

EazyBreezy said:

And which do I run on my linebackers (I run 6-1)

You almost certainly want Mid Zone KO, especially on SUBLBs and Slot corners.  In a perfect world, you'd have Peanut Tillman -- who gets both Flat + Mid Zone KOs for 0AP.  This is what truly sets Fred Warner apart as the only LB in the entire game that gets both Mid Zone + LurkArtist for 0AP.  Mid Zone covers a LOT of area on the field, it's more grass than Flat zone.  I typically find that almost all of the most annoying routes opponents run will be directly countered by Mid Zone KOs.  It activates a TON.

in 6-1 Mid Zone on both outside LBS and raw dog the user.

peatrick said:

You almost certainly want Mid Zone KO, especially on SUBLBs and Slot corners.  In a perfect world, you'd have Peanut Tillman -- who gets both Flat + Mid Zone KOs for 0AP.  This is what truly sets Fred Warner apart as the only LB in the entire game that gets both Mid Zone + LurkArtist for 0AP.  Mid Zone covers a LOT of area on the field, it's more grass than Flat zone.  I typically find that almost all of the most annoying routes opponents run will be directly countered by Mid Zone KOs.  It activates a TON.

6-1 doesn’t have slot corners it only has the 2 outside corners then the 3 linebackers one on each side then 1 in the middle

peatrick said:

You almost certainly want Mid Zone KO, especially on SUBLBs and Slot corners.  In a perfect world, you'd have Peanut Tillman -- who gets both Flat + Mid Zone KOs for 0AP.  This is what truly sets Fred Warner apart as the only LB in the entire game that gets both Mid Zone + LurkArtist for 0AP.  Mid Zone covers a LOT of area on the field, it's more grass than Flat zone.  I typically find that almost all of the most annoying routes opponents run will be directly countered by Mid Zone KOs.  It activates a TON.

MIdzone KO works great for LB knocking passes against quick verticals within the hashes. It is almost a necessity for LBs to have MZKO.

Id go flat zone for 61 outside lber and then mid zone on your middle linebacker

Your two outside lber wont be inside the hashmarks much......if at all

EazyBreezy said:

6-1 doesn’t have slot corners it only has the 2 outside corners then the 3 linebackers one on each side then 1 in the middle

Thanks, I obviously missed OP's comment about using 6-1, but the principles remain the same.  We match abilities to areas of grass on the field, at least that's how I approach my squad and roster building.  Perfect LBs (or Slot corners) would have both Mid and Flat Zone KO, but not a single one of those exists in the entire game, to the best of my ability, so Peanut Tillman remains THE gold standard, IMO.