I might also point out that your diagram in post #30 has a few errors, Dave.
The line you have labelled "1013ft", I assume you mean 1013 hPa. As it is a higher pressure than the pressure you have placed (correctly) at the field, it should be lower in the diagram than the field, not higher. (In fact, it should be between the field and the sea.)
For altimetry, "wind on pressure = wind on height." To wind on 21 mb, we wind on 630 feet. (that's wind as in wound-up, not wind, as in blow
)