What yeast? What temperatures? What gravity? How big of a starter?
I find that at warmer temperatures, with larger starters and moderate gravity worts I tend to have the highest krausen. It also depends heavily on the yeast strain too. Low gravity or high gravity tends to I guess have too little or too much sugar for the yeast to cause a lot of krausening.
I've never had a blow over in a carboy. Granted, I typically leave a lot of head space, but for example, I only left maybe 2 inches of head space in my 3 gallon carboy with a Pilsner I just did, didn't blow over and I had maybe half an inch at least of headspace over the level of krausening. That was probably my riskiest brew as I normally have about 3-5 inches of head space and my typical Krausen is 1.5-2 inches. I've had as much as 3 inches of krausen and as little as an inch. Some strains seem to cause a higher krausen and some lower, but temp, starter size and wort gravity also have a lot of impact on this (I have had starters in my flasks krausen over a couple of times).