The avo std ride height in truth drop around 3/4 " as I've used these myself, excellent spring, don't go stupid low imo, I'm on coilovers set at std height minus around 1" rear, 2" front,(higher rear works better).
A lot like the ahmed bayjoo springs, again excellent springs, prefer the avo myself, my dad has a old set of my avo on his 4i that I bought around 10 years ago!!
Spring breakage is very common on cars in general these days, caused by the lower level of sulphur in the metal mix for emissions reasons they don't flex as well as they used to.
For safety reasons ONLY change complete car set, ie all 4 springs.
tabetha