too big on the TB and they can get touchy too big on the plenum they get doughy.as far as oversizing like a carb its not as bad as you arnt trying to atomise fuel with airspeed through a carb.way massive big huge TB you could expect to see diminishing results purely from loss of airspeed through the TB

you also need to take into account TV cable for trans etc depending on what box you run.

as for injector placement generally aim them accross the short turn radius at the valve and the airstream will lift it away from the radius and hopefully cool the whole valve head.

in saying that its not allways easy to do with space constraints or port shape .just try to avoid spraying fuel straight at the port walls