Y-Offset of Cresc/Dim Lines

Default hairpin position is indeed not the same as default dynamic position, since hairpins are a different type of element. But for pretty much any element type, the easiest way to set defaults is make the adjustment you wnat in the Inspector, then press the "S" button right next to that control. The less easy was is Format / Style, then find the appropriate setting (Hairpins, Dynamics, etc). For some elements, you may nee to set the offset via the Text Style section.

Crescendo lines are in fact a type of hairpin. You can actually change them into regular hairpins by selecting it, scrolling to the bottom of the inspector, find Type under the Hairpin category, and change it from Crescendo line to Crescendo hairpin. For whatever reason, the default placement of these Hairpin lines is not controlled by the hairpin default.
As a workaround, click on one hairpin line, under the inspector, change your Y-Offset to the value you need, and the press the S button which sets it as the style default. For some strange reason, this default can't be edited from the Style menu.