Recently, somewhere on the internet (I forget where), I saw a question that was asking about the Hindrance height of a bridge, and an (obsolete) Q&A was referenced (for B6.2, I think). Just yesterday, though, I ran across a definitive answer on the heights of various Hindrances and wanted to document it for posterity's sake since I found it in an obscure place, and after a short search of the GS forums this seemed like the most relevant thread.
The text I found is located in footnote 3 from rule chapter P (Kampfgruppe Peiper): (it's also in footnote 6 of Pegasus Bridge)
3. 2.3 SLOPE LOS & ELVATION ADVANTAGE: Giving an Up-Slope unit a 3/4-level elevation advantage may seem overly complicated, but it in effect allows the unit to see over half-level--yet not over full-level--obstacles/Hindrances rising from the same Base Level as that unit. The "half-level" Hindrances referred to are brush, bridge, grain, marsh, crag and AFV/wrecks.