O.K. had a word with a seasoned Bobl/Shatz trader. Most people do 2:1
but it is a mugs game these days apparently, he shoudl know, he trades it.
Eurex works on first come first served basis as appose to Liffe which is pro-rata, so all these guys get in early and start stacking orders, if they get filled one side they do the other. There is not a lot of edge left in it as everybody is trying hard and the big boys will spoof the small player out much of the time.
Like I say this is what I was told by a guy who now trades more Curve spreads than inter market.