If I'm facing you w/ my arms at my sides, the head that is visible from the front [and the top head] are defined and rock hard. But the other head on the other side is basically just flab.
The lateral & medial (outer) heads that you've described as already tight are the primarily areas hit by dips, close-grip benches & pushdowns. They're all good substitutes for one another but won't address your problem.
To hit the long head, the largest part of the triceps, lying or seated extensions to behind the head, with the elbows raised up around eye level. Seated, leaning back slightly, with back braced. Do extensions after the dips, so that the elbows are already warmed up. Try both seated and lying, see which works better or alternate one and then the other every so often. Do the same number of sets of extensions as you are doing on dips, close-grips, pushdowns or kickbacks.
One-arm pulley kickbacks are also excellent; a downside is limitations in the amount of weight that can be used, in part due to the involvement and pre-exhaustion of the rear delts. Use of a pulley instead of a dumbbell takes much more of the rear delt out of it while hitting the tris more intensely. Try variations using either the low or mid-level pulley.
From what i'm reading you're training the same muscle every day?
If you work them hard you should be hitting them every 2-3 days at the most.
