I have been asked a few times, "Do I take the chest measurement across the bust or at the high bust area?" So I think it's time I answer that here.
The simple answer is that it is probably better to take the measurement in the high bust area.
Here is what Amy Herzog says about it in her book Knit to Flatter:
Your upper torso circumference [or high bust measurement] is the single most important measurement you can take when knitting sweaters because it can and should be used as your "full bust size" when selecting a "base" pattern size to knit for yourself. When you choose a size based on your upper torso circumference, all of your seaters will fit nicely in the hardest area of the sweater to modify: the shoulders.
This is true of the Phrancko Sweater pattern as well. The shoulder width is determined from the chest measurement and it is constant no matter what fit is chosen because your shoulders do not get wider just because you want to work a looser fit.
This is, in fact, one of the advantages of creating a custom-fit Phrancko Sweater pattern. Patterns published as Small, Medium, Large, etc. increase the shoulder width and all other measurements as you go up in size. Notice that the Phrancko sweater has only one size for shoulder width, neck width, and arm length for every fit because these measurements do not vary with ease.
If you have a sweater that fits the way you like, then after entering the high bust measurement for your chest circumference, simply measure the width of that sweater and choose the fit that gives the same chest measurement in the schematic on the page before you purchase it.
For large busted women however that may produce sleeves that are wider than desired (even though the shoulders will fit nicely). In that case, one could select a more standard fit to generate your "base" pattern and then modify it as necessary to either add darts or short rows in the front. The pattern does not describe how to do this so that depends on your ability to modify patterns to suit you. Again, I refer you to Amy Herzog's book for suggestions how to do that.
As a side note, remember this: Any and all inputs may be modified until you purchase the pattern. So pay careful attention to the schematic on the "Submit Payment" page. If anything does not suit you, click the "Change Sizes" button, then click other buttons to return to any page where you have input data. For instance, if you really think the shoulders are too narrow, go all the way back to your measurements and make the chest measurement larger. This will increase the shoulder width as well. Then choose a tighter fit to get the chest measurement back down to where you wanted it. Be careful though! The shoulder width may look narrow to you because the sleeves are set in. The mock seams between body and sleeve should be straight lines directly up from the underarm to the shoulder for a true set-in sleeve fit. So making this modification should only be done if you are experienced enough to know exactly how wide the shoulders should be for your set-in sleeved sweaters.