There is a natural tendency to limit the pronounced length of names, so a long 3 syllable name like
Solomon is rarely going to have a long first vowel, and this (usually) carries through to short forms like
Sol. This is a general rule for names in the Germanic-language world, long first-syllable names will generally be only one or two syllables, 3 syllable names will have all short syllables, no matter what language the name is from (unless it is recognizably foreign or unfamiliar), even if the third syllable was originally long. If necessary one or more vowels will be unvoiced or skipped altogether. of course the real difference between SAHL and SOUL is not value or length, but in the tendency of English-speakers to "break" a long o into a diphthong, reflected in the spelling (soul, bowl, coal - although in some of these cases the diphthong arose from an /o/ or /a/ followed by a /w/ and another unvoiced vowel).