Yeah I played around with that simulator yesterday. The idea that Kasich is going to average around 25% nationally is a bit of a stretch in my opinion. Reuters 5 day rolling polls show him at 9% as late as March 15. Also I don't think Cruz has a shot if it goes to a convention. Cruz is hated by the establishment of the GOP, and they are the ones who make up the convention. Everyday rank-and-file voters don't get invited to the Convention in Cleveland, so its going to be hard for Cruz to make a case when he's speaking to an audience that mainly loathes him. A contested convention favors Kasich or someone outside the political primary process - people have floated Paul Ryan and Mitt Romney.
You don't want a 1v1 if you want no one to get an outright majority before the convention-unless somehow voters start coalescing around Cruz real soon, he alone won't be able to pull that off.
It really depends on what triggers the contested convention- there's a (small) set of scenarios where Cruz has a delegate lead going into a contested convention, although that's only going to occur if Kasich drops out. It seems the theory that Trump has a 35% ceiling is going out the window. With every person who drops out he seems to pick up a small if not significant portion of their base, which has the effect of stalling any attempt to defeat him. If anything, my opinion has started to shift to the idea that maybe
Cruz has a 20% ceiling.
You've probably seen this article -
http://projects.fivethirtyeight.com/2016-endorsement-primary/Cruz has a huge problem in endorsements. For the guy supposedly the party's best chance to stop Trump before a contested convention, he seems to not be receiving any help.
I see your point though about a 1v1 potentially helping Trump. Even if Cruz beats Trump in outright % voting, he may not collect enough delegates to beat Trump due to proportional allocation.