The question raised has been an analysis of why one would use a direct raise convention rather than starting a 2/1 auction, and what inferences can be gleaned therefrom. The first issue discussed was the 12-14 splinter through a 3C raise, showing three or more of (a.) only one top trump, (b.) only one top card in the suit that would otherwise start the 2/1 auction, (c.) no honor in the stiff suit, and/or (d.) no control in the fourth suit. A 2/1 auction with a stiff, therefore, will show more than 14 HCP or that two or fewer of these four statements can be made.
The next question concerns the direct splinter, e.g., 1H-P-4C. This could be played in at least one of two ways.
One method that I have used is for this direct "shape bash" bid is used exclusively to handle voids on the side. This does have some merits, as hands with voids are often tough. If the range is still 12-14 (which makes sense), then the parameters of three of the four criteria for 3C...Splinter auctions also makes sense. You just will always know that one of the four (not an honor in the short suit) will always be present, of course.
Another method is for this call to show extra strength, perhaps roughly 15-16. I hate HCP ranges, because these make little sense to me. I often overlap for disclosure reasons. The hand is "15-16" if it looks like that playing strength.
In any event, the parameters of the "three of four" from above can be most easily tweaked for the direct splinter by increasing the strength of the trump contribution to two honors. Thus, whereas 3C...Splinter would typically show one top honor, plus the rest of the criteria being met, the direct splinter would show the same criteria but two top honors in trumps.
That appeals to me because these hands often start with a cuebid of three of the major, showing good trumps but nothing else to cuebid. It wastes a cue, as otherwise three of the major would also be a cue. An example. 1H-P-2C-P-2D-P-2H. Opener bids 2S. Responder, with something like QJx-AQxx-x-AJxxx, could not cuebid 2NT (poor trumps), 3C(two top trumps), or 3D(diamond A/K/A). He cannot Picture Splinter. So, he cuebids 3H, which becomes a redundancy because merely bypassing 2NT showed the two top hearts.
Direct splinters, which are "shape bash" bids, should be reserved from problem hands (voids) or for problem cuebidding hands. That serves two purposes, again. First, partner can better read your likely hand if you splinter. Second, partner can better read your necessary hand parameters if you do not splinter.