Aaaah, that makes sense and it doesn't sound too gimmicky. The current marker kind of does that - it indicates the area in which the ball will pitch. It does grow and shrink outside of that boundary though, so it's something I can introduce. Good idea!
As you say, it's basically what's happening anyway.
The potential for it is fairly big as well... for example -
The obvious setup wherein the better the bowler, the smaller the pulse. This seems to make sense for part-timers whereby getting it half-right each time leads to a potentially decent spell, but also a potentially atrocious spell.
This last point is important, because as a bowler gets hit for a few boundaries, or bowls a few wides, the pulse grows. Hit Steyn for 6 sixes in an over, and his pulse is going to suddenly seem like you're bowling with a part-timer. Each ball is tricky to get where you want because mentally he's shot. Of course, taking him out the attack for a certain amount of overs will see it slowly return to normal.
Hence you introduce the idea of taking bowlers out the attack. Attacking a part-timer to try and remove a relief bowler and put more pressure (strain, or literally their stamina and fitness). From here you can feasibly introduce mental strength as a statistic as well. The higher it is, the longer it takes for the pulse to expand under duress etc...
Again, back to thinking out loud and I'll leave it there :P