What's a good MIDI drumpad iOS app with *large* pads?

I'm constantly tapping out rhythms on my iphone (sadly it's no longer possible to lock the screen on a modern iphone for some reason, so I have to do my finger drumming on the back of the phone, but I digress..), and I've often wished that I could trigger drum samples this way. I like the feel of tapping on the screen, and in some ways I like it better than using drum pads on traditional midi controllers. But the problem is that all the drum sampler apps I've found have touch zones that are way too close together. Like I've tried drumming on that drumset in GarageBand and there's just no way. I'm always hoping they'll update it so you can zoom in on just a couple drums. It's big enough on an iPad, but I don't usually have an iPad on me.

So anyway, my question is -- can someone recommend a drum pad app with big pads? Like maybe something that divides the screen into just four rectangles? Also it's really important that the app is able to send midi data to other midi devices. Thanks.