Keep in mind the benefit of a flex is the improved read angle and range. By putting them so close you may still need to manipulate your hand to avoid a collision.
Is there any particular reason you want them all in 1 hand? The wrist / forearm is a great place for flexes.
Although it would depend on the readers you are using them with, if it is just phones that should be fine as the coils in them are not very powerful and you can easily manipulate the phone.
One thing I will say if you do put a flex in position 1, you would essentially be loosing the option to put a HF x form factor in position 0.
Shameless plug: This wiki post covers a lot of implant locations if you have not seen it.
Out of curiosity what is your use case for the FlexNT as both the FlexM1 and Apex will provide the same capabilities and much more? Is it purely that it will fit in pos 8?