Bench plane tuning question

So I've got a goofy issue tuning my block bench plane. It's one of the Pony Jorgensen #4 smoothing planes they're selling at Lowe's in the States. Works pretty well with one exception: Moving the frog forward to bring the iron closer to the mouth also advances the iron.

I can't get it anywhere near as closed as you're supposed to with a smoothing plane before I can't retract the iron sufficiently. The mating surface in the sole that the frog rests on is slightly angled downward, so the frog is lowered as it is moved forward. I can't realistically bring the iron any farther on the chip breaker than I've got it.

As I had it apart, I noticed the finish on the bottom of the frog, the surface that mates with the sole, was as cast, it isn't machined or lapped. Should it be?