One of the reasons people feel their front delts on flat is because they flare too much, perpendicular upper arm to chest equals stress on shoulders, check some powerlifting videos and look how they are bending angle just a lil further down, something like 45-75 degrees not 90. Now on incline positioning can differ, up to neck pressing helps "isolate" even if that is possible the upper pec, but it's not set in stone you have to go so high you can just perform incline like you do flat. Biggest reason for chest not being enough developed (after genes of course) is not enough weight, no exercise can really fill it in on it's own unless it grows naturally ergo weight progression. Using a smith is not so bad for performing half rom pressing but still it's better using free weight. Half rom bench press is something like board press, bar not all the way down onto chest, elbow not locked out. But as said above, use dumbbells because they require even more stabilizers and likely provide better and more even growth, altho weight is less. Of course dips and weighted dips (getting really frustrated when people call dips a bodyweight exercise, strap 100lb to your waist and go call yourself 300lb) are good if not mandatory exercise.
