Just thought of a couple of other points, I am usually trying to get 25L in the FV and to achieve that with the large dead space and gunk that ends up blocking the drain off, typically I sparge right to the top marker I can't recall what that mark is, but boil off with the 1 larger elemt on is about 3L per hour, also it takes just about bang on 40 mins to go from mash temps to boiling with both elements on.
So if your using the step timer as I do and you want a 90 minute boil, add another 40 mins to that step as unlike the Klarstein it counts down straight away, not when it gets up to temperature.
Also I went from Klarstein to Brewzilla and the smaller diameter malt pipe makes boil overs and foam as it approaches the boil catch you out much more quickly, I keep a bowl and a sieve handy to scoop it off the top